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Selina Concise Biology Class 7 ICSE Solutions – Nervous System

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Biology Class 7 ICSE Solutions – Nervous System

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Biology. You can download the Selina Concise Biology ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Biology for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Biology ICSE Solutions Chemistry Physics Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 7 Biology Chapter 6 Nervous System

Synopsis —

The interaction of these activities of a living being as per the needs of the body internally or externally is called coordination.
Nervous coordination is brought about by the nervous system which is made up of the brain, spinal cord, nerves and the sense organs.
Chemical coordination is brought about through chemical messengers called hormones.
The nervous system is made up of special cells called nerve cells or neurons.
The end of the axon terminates in a number of branches called terminal branches.
The terminal branches of the axon of one neuron lie very close to the dendrites of another neuron. This point of contact is called a synapse.
A nerve is formed of a bundle of axons (nerve fibres) enclosed in a tubular medullary sheath. There are three kind of nerves as describe
1. sensory nerve
2. motor nerve
3. mixed nerve.
The nervous sytem of human beings consists of the following three systems:
1. The central nervous system
2. The peripheral nervous system
3. The autonomic nervous system
The brain has three main parts:
1. The cerebrum
2. The cerebellum, and
3. The medulla oblongata
The main functions of the spinal cord are:
1. To control reflexes below the neck.
2. To conduct messages from the skin and muscles to the brain.
3. To conduct commands from the brain to muscles of the trunk and limbs.
The autonomic nervous system consists of a pair of chain of nerves and ganglia found on either side of the backbone. This system controls the involuntary activities of the internal organs.
Stimulus: Any change in the environment that usually results in change in the activity of the body.
Response: The activity of the body in response to a received stimulus.
Impulse: A wave of electrical disturbance that runs through the nerves.
Receptors : These are sense organs which receives the stimulus.
Effector: Any muscle or gland where the response occurs.

Review Questions

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Medulla oblongata controls
(i) Smelling
(ii) Beating of heart and respiratory movement
(iii) Intelligence and will power
(iv) Balancing the body

(b) Spinal cord is an extention of:
(i) Cerebellum
(ii) Cerebrum
(iii) Vertebral column
(iv) Medulla oblongata

(c) Body posture is mantained by:
(i) Cerebellum
(ii) Cerebrum
(iii) Medulla oblongata
(iv) Spinal cord

Short Answer Questions:

1. Write one word in the space provided to complete the second pair of the related words pertaining to nervous system.
Memory: cerebrum:: breathing:
Balance: cerebellum:: reasoning:
Answer:
Memory: cerebrum: beathing: medulla oblongata
Balance: cerebellum:: reasoning: cerebrum

2. (a) Name three major divisions of the human nervous system.
Answer:

The central nervous system (brain and spinal cord)
The peripheral nervous system
The autonomic nervous system

(b) Name the three main parts of human brain.
Answer:

Cerebrum
Cerebellum
Medulla oblongata

3. Given here is the diagram of a neuron. Name the parts numbered 1-6.
Selina Concise Biology Class 7 ICSE Solutions - Nervous System 1

Answer:

dendrite
dendrite (Terminal Arborization)
nucleus
axon (Nerve fibre)
cell Body (cyton)
node of ranvier
sheath

Long answer questions

Question 1.
With the help of a suitable diagram describe the structure of a neuron.
Answer:

Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.

The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.

The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this:
Organ → Message goes to dendrites →Cell body → Axon → Muscles or glands

Question 2.
Briefly describe the structure of the cerebrum in human brain, and mention its functions.
Answer:
Brain consists of main three parts and lies in the cranial cavity of skull.

The cerebrum
The cerebellum
The medulla oblongata

Cerebrum — It is very large and form two third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.
Functions:

It controls all the voluntary activities.
It is the seat of intelligence, consciousness and will power.

Question 3.
Mention the three functions of spinal cord.
Answer:
Spinal cord has the following functions.

It is the centre of reflex actions below the neck.
It carries messages from the skin and muscles to the brain.
All the stimuli and responses are passed from and to the brain through the spinal cord.

Question 4.
Describe three kinds of nerves, giving example of each.
Answer:
A nerve is formed by a group of nerve fibres (axons) encased
by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons (nerve fibres) We have three kinds of nerves:

Sensory nerve — It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
Motor nerves—These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eye ball.
Mixed nerve — It has both sensory and motors fibres as nerve going to the tongue.

Question 5.
What are voluntary and involuntary actions ? Which part of the nervous system controls them ?
Answer:
Voluntary action: When an action is produced with the involvement of thoughts, they are called the voluntary action. For example, writing an article jumping from heights. These actions are produced consciously by our body.
Involuntary action: Actions which take place without consciousness or willingness of an individual are called the involuntary action. Digestion, heart beating, sneezing, etc are few examples of involuntary actions.

The cerebral cortex controls our voluntary actions like running and walking etc.
Medulla helps in involuntary actions like hearbeat, breathing etc.

Additional Questions

I. Multiple choice questions. Tick (✓) the correct choice:

I. Nervous system in humans consists of
(a) brain and nerves
(b) brain and spinal cord
(c) brain, spinal cord and nerves
(d) none of the above.

II. Fill in the blanks:

Basic structural unit of the nervous system is the neuron.
Central nervous system consists of brain and spinal cord.
A neuron consists of cell body, dendrite and axon.
The neurons carrying impulses from the brain to the muscles are called motor or efferent neurons.
Peripheral nervous system consists of nerves.
The three main parts of the brain are cerebrum, cerebellum and medulla oblongata (brain stem).

III. State whether the following statements are true (T) or false (F):

1. Each neuron consists of three parts called cell body, cyton and axon.
False. Each neuron consists of three parts called cell body, dendrite and axon.

2. The largest part of the brain is the cerebrum.
True.

3. Cerebellum maintains balance of the body.
True.

4. There are 31 pairs of cranial nerves.
False. There are 12 pairs of cranial nerves.

IV. Find the odd-one out, giving reasons:
Axon, cell body, dendrite, cerebellum
Ans. Cerebellum is the odd one out as it is a part of brain while rest three are parts of a neuron.

V. Define the following:
1. Reflex arc
2. Sensory neuron
3. Motor neuron
4. Neuron
Answer:

Reflex arc: The path that an impulse takes in a reflex action is called a reflex arc.
Sensory neuron: The neurons which carry impulses
from the body parts to the spinal cord or the brain are called sensory or afferent neurons. For example, optic nerve of the eye.
Motor neuron: The neurons which carry impulses from the brain or spinal cord to the body parts are called motor or efferent neurons.
Neuron: A neuron or a nerve cell is the basic structural and functional unit of the nervous system.

VI. Answer the following:

Question 1.
Describe the two parts of the nervous system.
Answer:
The nervous system of human has two parts:

Central Nervous System (CNS): It consists of the brain and the spinal cord. The brain lies protected inside the skull while the spinal cord is protected within the vertebral column.
Peripheral Nervous System (PNS): It consists of nerves arising from the spinal cord (spinal nerves) and the brain (cranial nerves). These nerves link the central nervous system with the various body organs.

Question 2.
What are nerves? Mention the types of nerves found in humans.
Answer:
A bundle of nerve fibres joined together as a tubular sheath that transmits impulses between brain or spinal cord and other body parts is called a nerve. The nerves constitute the peripheral nervous system.
Nerves are of two types in humans:

Cranial nerves: They emerge from the brain. There are 12 pairs of cranial nerves.
Spinal nerves: They emerge from the spinal cord. There are 31 pairs of spinal nerves.

Question 3.
Explain the structure of brain.
Answer:
The brain is the main control centre of the nervous system.
It is enclosed within the bony shell of cranium.
It consists ofthree main part:

1. Cerebrum: It is the uppermost and largest part with many ridges and grooves. It is divided into right and left halves called cerebral hemispheres. It controls our thinking, reasoning, intelligence, memory and perception of pain, sound, touch, taste and smell.
2. Cerebellum: It is located under the cerebrum at the back of the head. It maintains balance of the body and coordinates muscular activity.
3. Brain stem (medulla oblongata): It joins the brain to the spinal cord. It controls the activity of internal organs like heartbeat and breathing.

Question 4.
Compare the nervous system and the endocrine system.
Answer:
Nervous system

Messages are sent through nerve fibres.
It consists of brain, spinal cord and nerves.
No hormones are secreted. Messages are sent as impulses.
Transmission of impulse is quick.

Endocrine system

Messages are sent through blood in the form of hormones.
It consists of endocrine glands.
Hormones secreted by glands regulate the body activities. .
Transmission takes time.

Selina Concise Chemistry Class 6 ICSE Solutions – Matter

August 11, 2022December 5, 2019 by Prasanna

Selina Concise Chemistry Class 6 ICSE Solutions – Matter

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Chemistry for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Chemistry ICSE Solutions Physics Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 6 Chemistry Chapter 3 Matter

POINTS TO REMEMBER

Horse, mango tree, dog, animals, plants are living, while stone, pen, glass, water, book, table, air are non-living.
All the above mentioned things living and non-living are matter.
Energies like light, sound, heat are not matter, as these have no mass.
Matter : “Anything that has mass and occupies space is called matter.” Matter (mass) remains same at all places.
Molecules of matter are in motion.
The things which are similar in one or more ways are grouped together and this practice is classification.
There are inter-molecular gaps (spaces) and inter-molecular attraction (force of attraction) between molecules.
Solids are rigid, have definite volume, retain their shape and are incompressible.
Liquids can flow, have definite vol., have no definite shape. Have only one free surface.
Gases Have no definite volume, no definite shape can flow are compressible.
Inter-molecular force : Solids > Liquids > Gases.
Inter-molecular volume : Solids < Liquids < Gases.

Activity 1

Question 1.
List five substances made using each of the following materials:
Answer:

Wood : Chair
Paper : Book
Plastic : Bucket
Metals : Copper wire
Leather : Shoes
Cloth : Shirt or bag

EXERCISE- I

Question 1.
Define matter.
Answer:
Anything that has mass and occupies space is called matter.

Question 2.
What are the two main types of matter? Give two examples for each type.
Answer:
The two main types of matter are :

Living matter: The earth is home to all kinds of plants and animals. They can grow, move and reproduce on their own. Examples : Plant, lotus, animals, human etc.
Non-living matter : Most of the matter in the universe is non-living. It means that it does not grow, move or reproduce on its own. It can be natural or man made.

(a) Natural matter: It occurs in nature and can be used to make more useful substances, e.g., wood, coal, silk, water, stone, cotton, jute, cereals, fruits, etc.
(b) Man-made matter : It is produce artificially from natural matter, e.g., plastics, soaps, detergents, medicines, glass, nylon, steel, ceramic, etc.

Question 3.
Differentiate between living and non-living matter.
Answer:
Living matter:

The earth is home to all kinds of plants and animals. They can grow, move and reproduce on their own.
It is natural only.

Non-living matter:

Most of the matter in the universe is non-living. It means that it does not grow, move or reproduce on its own.
It can be natural or man made.

Question 4.
Select natural and man made matter from the following
list: Wood, plastic, silk, medicines, detergents, coal, water, ceramic, cotton, glass, nylon, fruits.

Answer:
Natural matter: Wood, silk, coal, water, fruits.
Man made matter: Plastic, medicines, detergents, ceramic, cotton, glass, nylon.

EXERCISE-II

Question 1.
Name the smallest particle from which matter is made up.
Answer:
The smallest particle from which matter is made up is atom.

Question 2.
What are molecules ?
Answer:
Molecules are the smallest unit of matter. They exhibit all the properties of that kind of matter and is capable of independent existence.

Question 3.
Give one difference between atoms and molecules.
Answer:
Atoms may or may not have independent existance. While molecules have independent existence.

Question 4.
Define:
(a) Intermodular force of attraction.
(b) Intermodular space.

Answer:
(a) The molecules of matter are always in motion and attract each other with a force, and this force is called intermodular force of attraction due to which they are held together.
(b) The molecules can move only when there are gaps or space between them, this space is called intermodular space.

Question 5.
Name the three states of matter and define them.
Answer:
The three states of matter are :

Solid State
Liquids
Gases :

Solid State : The molecules are very close to each other hence intermodular spaces are small and intermodular force is strong.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 1
Hence solids have definite volume, rigid, retain definite shape and are incompressible.
Liquids : The molecules are less closely packed have more intermolecular spaces than solid, less stronger forces than solids.

Hence liquids have definite volume but no definite shape. They take the shape of container in which they are put.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 3
Gases : The molecules in the gases are far apart with weakest force of attraction. Hence gases have neither definite volume nor definite shape but easily compressible.

Question 6.
What are fluids ? Give two examples
Answer:
Substances that can flow are called fluids. Both gases and liquids are fluids, e.g. gases (carbon dioxide, hydrogen), liquids (water, petrol and sulphuric acid).

Question 7.
Classify the following into solids, liquids and gases.
Oxygen, milk, common salt, wax, stone, L.P.G, carbon- dioxide, sugar, mercury, coal, blood, butter, copper, coconut oil, kerosene.
Answer:
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 4

Question 8.
Give reasons
(a) Liquids and gases flow but solids do not ?
(b) A gas Alls up the space available to it.
(c) The odour of scent spreads in a room.
(d) We can walk through air.
(e) Liquids have definite volume but no definite shape.
(f) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged.
(g) When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.
(h) A red ink drop added to small amount of water in a glass turns the water red in some time.

Answer:
(a) The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps*in solid molecules is less and molecular force of attraction very strong.
(b) Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them.
(c) Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room.
OR
Due to inter-mixing of scent molecules and air molecules, scent fumes spread into the room.
(d) The molecules of air are far apart i.e. large gaps and we can walk through air easily.
(e) The molecules of liquid are loosely packed and intermolecular force of attraction is small but number of molecules in it remain the same. Hence liquids have definite volume but no definite shape.
(f) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged because the sugar particles are adjusted between the water molecules as inter-molecular gaps are more in liquids.
(g) This is because Gases can diffuse or flow in all directions.
(h) When we put a drop of red ink in a glass of water, its particles diffuse with particles of water slowly but continuously and the water turns red.

Question 9.
Define:
(a) cohesive force
(b) diffusion
(c) Brownian movement

Answer:
(a) Cohesive force : The force of attraction between particles of the same substance is called cohesive force.
(b) Diffusion: The phenomenon of intermixing of particles of one kind with another kind is called diffusion.
(c) Brownian movement: The zig-zag motion of particles suspended in a medium is called Brownian movement

Question 10.
Why is an egg kicked out of a bottle when air is blown inside the bottle?
Answer:
When we invert the bottle and blow air into the bottle throw the side opening. It creates high pressure inside the bottles and the egg is kicked out of the bottle.

EXERCISE-III

Question 1.
State the three effects of heat on matter.
Answer:
When a substance is heated, it can cause.

Interconversion of states of matter.
Thermal expansion of the substance.
Chemical change.

Question 2.
(a) Define : interconversion of states of matter.
(b) What are the two conditions for the interconversion of states of matter ?

Answer:
(a) The process by which matter changes from one state to another and back to original state, without any change in its chemical composition.
(b) Two conditions are :

Change in temperature
By applying pressure

Question 3.
Define the following terms:
(a) Fusion
(b) Vaporisation
(c) Condensation
(d) Sublimation
(e) Diffusion
(f) Melting point
(g) Boiling point
(h) Liquefaction

Answer:
(a) Fusion : The heating process by which a solid changes into the liquid state is called fusion.
(b) Vaporisation : The heating process by which a liquid changes into its vapour state is called vaporisation.
(c) Condensation : The process by which a substance in gaseous state changes into its liquid state is called condensation.
(d) Sublimation: The change of solid on heating to vapours directly and vice-versa without passing through the liquid state is called sublimation.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 5
(e) Diffusion : The phenomenon of intermixing or spreading of gaseous molecules is called diffusion.
(f) Melting point: The fixed temperature at which a solid changes into a liquid at a given pressure is called its melting point. The temperature remains constant as long as the conversion is going on.
(g) Boiling point: The fixed temperature at which a liquid starts changing into gaseous state is called its boiling point. The temperature remains constant till the whole of the liquid changes into gaseous state.
(h) Liquefaction : Change of vapours on cooling to liquid is called liquefaction.

Question 4.
Differentiate between:
(a) Solidification and condensation
(b) Melting and boiling
(c) Gas and vapour
(d) Miscible and immiscible liquids.

Answer:
(a) Solidification : The process of changing liquid into a solid state by cooling is known as solidification.
Example : water → ice.
Condensation : The process of changing a gas or vapour state to a liquid state by cooling is known as condensation. Example : steam → water.
(b) Melting : The fixed temperature at which a solid changes into a liquid at a given pressure is called its melting point.
e.g. ice → water.
Boiling : The fixed temperature at which a liquid starts changing into gaseous state is called its boiling point.
e.g. water → steam.
(c) Vapourisation : The process by which a substance changes from a liquid state to vapour state is called vaporisation or evaporation.
e.g., Water changes into gaseous state on heating.
Gas : The substance which remain in the gaseous state under normal conditions of temperature and pressure are called gases.
e.g, Oxygen, hydrogen, nitrogen.
(d) Miscible: Liquids which mix with each other are called miscible liquids. Example : Water and alcohol.
Immiscible liquids : Liquids which do not mix with each other are called immiscible liquids. Example Water and oil.

Question 5.
Give reasons :
(a) How is interconversion of states of matter different from chemical reaction ?
(b) Why a solid does not flow, but a liquid flows ?
Answer:
(a) During interconversion of state of matter composition
of substance remains the same matter changes from one state to another and back to the original state, while chemical reaction involves re-arrangement of the molecular structure and composition changes.
(b) In solids there is a strong force of attraction between the molecules and the space between them is very negligible. The molecules are therefore, not free to move. They merely vibrate about their mean positions. But in the case of liquids, the molecules are not very closely packed. They do not attract each other as strongly as the molecules of solids. Thus, the intermolecular spaces are larger and the molecules are able to move about more freely. This makes a liquid flow.

Question 6.
How does a liquid changes into its gaseous state? Explain ?
Answer:
As a liquid is heated, its particles starts gaining energy and move more vigorously which increases the gaps between the particles and decreasing the force of attraction. Ultimately a liquid changes into gaseous state.

Question 7.
Water cycle is an example of interconversion of states of water. Explain.
Answer:
Water from oceans, rivers, lakes from leaves of trees (transpiration) changes into vapours when temperature increases or evaporates and enters the atomsphere as clouds when temperature falls the vapours change into water and some of it in the form of snow fall on mountains and earth in the form of water and hales and this continues. Thus water cycle is example of interconvertion of states of water.

Question 8.
What happens to a metal ball when it is heated? What does this show?
Answer:
When metal ball is heated, it expands. This can be proved by following experiment:
Take a metallic ring and ball. Try to pass the metal ball through the ring. The ball is able to pass through the ring. Now heat the metal ball for 5-6 minutes. The hot ball is not be able to pass through the ring.
This shows that a solid expands on heating. Now cool the ball, it again passes through the ring. This shows that a solid contacts on cooling.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 6

Question 9.
Why does a candle become smaller on burning with time?
Answer:
On heating, candle wax melts, then turns into vapour which reacts with air to produce two new substances, carbondioxide and water.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 7
Therefore a candle on burning becomes smaller and smaller and the part of wax which has undergone chemical change cannot be recovered.

OBJECTIVE TYPE QUESTIONS

Question 1.
Fill in the blanks :

(a) Water is a matter because it has mass and occupies space.
(b) Any matter which has a definite volume but no definite shape is called a liquid.
(c) Liquids and gases can flow.
(d) The molecules are at a greater distance in gases compared to liquids.
(e) Water boils at 100 °C.
(f) The physical state of a substance, which has neither fixed volume nor fixed shape is a gas.

Question 2.
Write whether the following statements are true or false.

(a) Only water can exist in three different states.
(b) If the container in which a gas is collected has an opening, the gas will flow out and spread itself indefinitely.
(c) Solids have the large inter-molecular space.
(d) There is no difference between evaporation and boiling.
(e) All solids, on heating, first change to the liquid and then to the gaseous state always.
(f) The intermolecular force of attraction is the weakest in gases.
(g) A gas has no free surface.

Answer:
(a) True
(b) True
(c) False
Correct: Solids have the very small (negligible) inter-molecular space.
(d) False
Correct : There is a difference between evaporation and boiling.
(e) False
Correct : Few solids, on heating, first change to the liquid and then to the gaseous state always.
(f) True
(g) True

Question 3.
For each of the following statements, say whether it describes a solid, a liquid or a gas.

(a) Particles move about very quickly but do not leave the surface : Liquid
(b) Particles are quite close together : Solid
(c) Particles are far apart and move in all directions : Gas

Question 4.
Match the following :
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 8

Question 5.
Name the phenomenon which causes the following changes:
(a) Formation of water vapour from water.
(b) Disappearance of camphor when exposed to air.
(c) Conversion of ice into water.
(d) Conversion of water into steam.

Answer:
(a) Formation of water vapour from water is vaporisation.
(b) Disappearance of camphor is sublimation.
(c) Conversion of ice into water is melting.
(d) Conversion of water into steam is boiling.

Question 6.
Give two examples for each of the following :
(a) Substances which sublime.
(b) Substances which do not change their states.
(c) Substances which are rigid and not compressible.

Answer:
(a) Naphthalene, camphor, dry ice.
(b) Oxygen, hydrogen, nitrogen
(c) Glass, stone, pen.

MULTIPLE CHOICE QUESTIONS

1. Which one is a kind of matter :
(a) light
(b) petroleum
(c) sound
(d) heat

2. the state of matter which has no definite shape or volume is called
(a) solid
(b) liquid
(c) gas
(d) water

3. There are large intermolecular gaps in
(a) water
(b) iron ball
(c) common salt ..
(d) air

4. All kinds of matter
(a) occupy space and have a definite mass
(b) have mass and a definite shape
(c) can change their states
(d) have a definite volume

5. A kind of matter which can sublime is
(a) water
(b) plastic
(c) milk
(d) iodine

6. A substance which can change its state
(a) wood
(b) oxygen
(c) paper
(d) cloth

7. The process by which a solid changes into a liquid is called
(a) freezing
(b) melting
(c) condensation
(d) evaporation

PROJECT

Question 1.
Fill the following chart showing twelve solids, twelve liquids, four gases and eight materials.
Answer:
Solids : (1) Mobile. (2) Pen. (3) Pair of shoes. (4) A T.V. set (5) Chair. (6) Telephone. (7) Remote control. (8) Wood. (9) Ornaments. (10) Scissors. (11) Eraser. (12) Mirror.
Liquids : (1) Ink. (2) Water. (3) Lemon juice. (4) Cough syrup. (5) Mouth wash. (6) Petrol. (7) Kerosene oil. (8) Spirit. (9) Thinner. (10) Mercury. (11) Milk. (12) Copper sulphate solution.
Gases : (1) Hydrogen. (2) Oxygen. (3) Sulphur dioxide. (4) Chlorine gas.
Materials : (1) Paper. (2) Wood. (3) Iron nails. (4) Cement. (5) Tiles. (6) Plaster of paris. (6) Sand. (7) Iron rods. (8) Bricks.

Question 2.
Think and try to find a way to demonstrate water cycle in class.
Answer:
Do it yourself.

Question 3.
To identify materials of common use
Procedure – Just move around in your house – in the drawing room, sitting room, bedroom, kitchen, bathroom etc.
Identify the things and All in the blanks in the table given below:

Study room
Drawing room
Kitchen
bathroom
another place

S.No. Place	Name of the thing	Material used for making the thing
Study room Drawing room Kitchen bathroom Any other place

Answer:

S.No. Place	Name of the thing	Material used for making the thing
1. Study room	Table, chair, books pens, pencils, table lamp, computer, fan	Wood, plastic, paper, glass, bakelite, connecting wires made of metal and plastics
2. Drawing room	Sofa, table, chairs, fan, curtains, windows etc.	Wood, cloth, coir, paint, plastics, aluminium, glass etc.
3. Kitchen	Taps, wash basin, cupboards, utencils, heating vessels strainer, containers aqua pure etc.	Steel, aluminium, glass, china clay, iron, plastic, copper, stainless steel, brass etc.
4. Bathroom	Taps, tubs, mugs, tooth brush, tooth paste, soap, pail etc.	Iron, brass, stainless steel, plastics etc.
5. Any other place	Scooter, car, road, rooms, trucks, shops.	Iron, rubber, coaltar, bricks, wood, plastics, clothes.

Selina Concise Physics Class 7 ICSE Solutions – Motion

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Physics Class 7 ICSE Solutions – Motion

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Physics for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Physics ICSE Solutions Chemistry Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 7 Physics Chapter 2 Motion

Points to Remember
Motion— Motion is the change in position with respect to a set of stationary landmarks.
Types of motion are translatory, rotatory and oscillatory.
A body is said to move in a translatory motion if the whole body moves through the same distance in the same interval of time.
A body is said to be in rotatory motion if it moves about a fixed point without changing the radius of its motion.
A body is said to be in oscillatory motion if it moves to and fro about its mean position.
A body is said to be in vibratory motion if the body moves to and fro in a particular style.
Oscillation of pendulum is one complete to and fro motion.
The maximum displacement on either side of a mean position is called amplitude.
A motion which repeats itself at regular intervals of time is called periodic motion.
A physical quantity which has only magnitude and no direction is called a scalar quantity.
A physical quantity which has magnitude as well as direction is called a vector quantity.
Speed is the distance travelled per unit time. It is a scalar quantity.
The displacement per unit time is known as the velocity of the body. It is a vector quantity.
The rate of change of velocity is called acceleration. It is a vector quantity.
Frequency is the number of complete oscillations in one second.
Unit of frequency is Hertz.
Motion is of two types (a) uniform (b) non-uniform motion.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) Two trains going in opposite directions with the same speed are at rest relative to each other.
Answer. False.

(b) A ball is thrown vertically upwards. Its motion is uniform throughout.
Answer. False.

(c) The motion of a train starting from one station and reaching at another station is non-uniform.
Answer. True.

(d) A motion which repeats itself after a fixed interval of time is called periodic motion.
Answer. True.

(e) A ball thrown by a boy from a roof-top has oscillatory motion.
Answer. False.

(f) Mass has both magnitude and direction.
Answer. False.

(g) .Weight always acts vertically downwards.
Answer. True

(h) Mass varies from place to place but weight does not.
Answer. False

2. Fill in the blanks

(a) Two boys cycling on the road with the same speed are at rest relative to each other.
(b) The motion in a straight line is rectilinear motion.
(c) One to and fro motion of a clock pendulum takes time = 2 s
(d) 36 km h^-1 = 10 m s^-1
(e) Total distance travelled = average speed × total time taken.
(f) The weight of a girl is 36 kgf. Her mass will be 36 kg.
(g) The weight of a body is measured using a spring balance.

Activity

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 1

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 2

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 3

3. Match the following

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 4

4. Select the correct alternative

(a) A book lying on a table is an example of

a body at rest
a body in motion
a body neither at rest nor in motion
none of these

(b) The motion of a pendulum is

rotatory
oscillatory
curvilinear
rectilinear

(c) A car moving on a straight road is an example of

rotatory motion
rectilinear motion
oscillatory motion
periodic motion

(d) A ball falls down vertically. Its motion is

periodic
linear
circular
vibratory

(e) If a body covers equal distance in equal interval of time, the motion is said to be

uniform
non-uniform
oscillatory
rotatory

(f) A boy goes from his house to school by bus at a speed of 20 km h^-1 and returns back through the same route at a speed of 30 km h_1. The average speed of his journey is

24 km h^-1
25 km h^-1
30 km h^-1
20 km h^-1

(g) The earth attracts a body of mass 1 kg with a force of 10 N. The mass of a boy is 50 kg. His weight will be

50 kg
500 N
50 N
5 N

B. Short/Long Answer Questions

Question 1.
Explain the meaning of the terms rest and motion.
Answer:
Rest— A body is said to be at rest if it does not change its position with respect to its immediate surroundings.
Motion— A body is said to be in motion if it changes its position with respect to its immediate surroundings.

Question 2.
Comment on the statement ‘rest and motion are relative terms’. Give an example.
Answer:
Imagine you are sitting inside a moving bus. When you look outside you will observe that you are moving. Now look to the roof of the bus. With respect to the roof of bus, you are at rest. Hence it is concluded that rest and motion are relative terms.

Question 3.
Fill in the blanks using one of the words : at rest, in motion.
(a) A person walking in a compartment of a stationary train is relative to the compartment and is relative to the platform.
(b) A person sitting in a compartment of a moving train is relative to the other person sitting by his side and is relative to the platform.
Answer:
(a) A person walking in a compartment of a stationary train is in motion relative to the compartment and is in motion relative to the platform.
(b) A person sitting in a compartment of a moving train is at rest . relative to the other person sitting by his side and is in motion relative to the platform.

Question 4.
Name five different types of motion you know.
Answer:
The different types of motion are :
1. Translatory motion
2. Rotatory motion
3. Oscillatory motion
4. Vibratory motion
5. Periodic motion
6. Multiple motion
7. Random motion.

Question 5.
What do you mean by translatory motion ? Give one example.
Answer:
If an object like a vehicle, moves in a line in such a way that every point of the object moves through the same distance in the same time, then the motion of the object is called translatory motion.
Example :
The motion of an apple falling from a tree, the motion of a man walking on a road, the motion of a box when pushed from one comer of a room to the other, are all the translatory motion.

Question 6.
Explain the meanings of (i) rectilinear motion, and (ii) curvilinear motion. Give one example of each.
Answer:
(i) Rectilinear motion — If the motion of a body is along a straight line, it is said to be the rectilinear or linear motion. The motion of bullet fired from a gun.
(ii) Curvilinear motion — If the motion of a body is along a curved path, it is said to be the curvilinear motion. For example, the motion of a cycle while taking a turn on the road, a car moving along a curved path, a ball thrown by an athlete are in curvilinear motion.

Question 7.
What is rotatory motion ? Give two examples.
Answer:
Rotatory motion— A body is said to be in a rotatory motion or a circular motion if it moves about a fixed axis without changing the radius of its motion.
Examples : The blades of a fan, a spinning wheel.

Question 8.
What is meant by circular motion ? Give one example.
Answer:
The motion of a body along a circular path is called circular motion.
Example : A girl is whirling a stone tied at the end of a string in a circular path.

Question 9.
How does a rotatory motion differ from the circular motion?
Answer:
(i) In rotatory motion, the axis of rotation passes from a point
in the body itself whereas in circular motion, the axis of revolution passes through a point outside the body. Thus the motion of earth around the sun is the circular motion whereas the motion of earth about its own axis is the rotational motion.
(ii) In the circular and rotatory motions, the distance of a point of a the body from a fixed point always remains same, whereas it is not same in curvilinear motion.

Question 10.
Explain oscillatory motion by giving one example.
Answer:
Oscillatory motion— The to and fro motion of a simple pendulum is an oscillatory motion.
Example : 1. The motion of a swing, 2. Piston of an engine.

Question 11.
What is vibratory motion ? Give one example.
Answer:
In vibratory motion, a part of the body always remains fixed and the rest part moves to and fro about its mean position. During the vibratory motion, the shape and size of the body changes. Example : When we breath, our chest expands and contracts. This motion is vibratory motion.

Question 12.
Differentiate between periodic and non-periodic motions by giving an example of each.
Answer:
Periodic motion : A motion which gets repeated after regular intervals of time is called a periodic motion.
Examples : The earth moving around the sun takes 365 days to complete one revolution and this motion gets repeated after every 365 days.
Non-periodic motion : The motion which does not repeat itself after regular interval of time is called non-periodic motion.
Examples : A footballer running on a field, application of brakes in a moving vehicle, a ball rolling down the ground gradually slows down and finally stops, motion of tides in the sea, etc.

Question 13.
What is random motion. Give one example.
Answer:
Random motion— When an object in a motion has no specific path and which suddenly changes its motion is said to have a random motion.
Example : A flying kite.

Question 14.
Name the type/types of motion being performed by each of the following:
(a) Vehicle on a straight road
(b) Blades of an electric fan in motion
(c) Pendulum of a wall clock
(d) Smoke particles from chimney
(e) Hands of a clock
(f) Earth around the sun
(g) A spinning top.
Answer:
(a) Rectilinear motion
(b) Rotatory motion
(c) Oscillatory motion, periodic motion
(d) Non-periodic motion
(e) Uniform circular and periodic motion
(f) Rotatory motion, circular motion and periodic motion
(g) Rotatory motion

Question 15.
Give two examples to illustrate that a body can have two or more types of motion simultaneously.
Answer:
Sometime a body can have more than one type of motion. Such a motion is called the mixed motion.
Example :
(i) The wheels of a moving train have both the translatory as well as the rotatory motions as it moves from position A to position B while rotating.

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 6
(ii) The earth rotates about its axis (rotatory motion) and at the same time it revolves around the sun in a curved path (curvilinear or circular motion) in a fixed time interval (periodic motion).

Question 16.
State the types of motion of the following :
(a) The needle of a sewing machine
(b) The wheel of a bicycle
(c) The drill machine
(d) The carpenter’s saw
Answer:
(a) Periodic motion
(b) Rotatory motion
(c) Mixed = Translatory and Rotatory motion
(d) Mixed = Translatory and Oscillatory motion

Question 17.
Distinguish between uniform and non-uniform motions, giving an example of each.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 7

Question 18.
How do you determine the average speed of a body in non-uniform motion ?
Answer:
In a non-uniform motion, the average speed of a body is calculated by dividing the total distance travelled by the body, with the total time of its journey. Thus,
Average speed = Total distance travelled by the body / Total time of joumey

Question 19.
Define the term weight and state its S.I. unit.
Answer:
The weight of a body is the force with which earth attracts the body i.e. the weight of a body is the force of gravity on it. The weight of a body is not constant, but it changes from place to place. It is represented by the symbol W. The S.I. unit of weight is newton (N).

Question 20.
How are the units of weight, kgf and newton related ?
Answer:
1 kg F = 10 N

Question 21.
State three differences between mass and weight.
Answer:
Mass

It is the quantity of matter contained in a body.
Its S.J. unit is kilogram (kg)
It is constant for a body and it does not change by changing the place of the body.
It is measured by a beam balance.

Weight

It is the force with which the earth attracts the body.
Its S.I. unit is newton (N) and other unit is kilogram-force (kgf) where 1 kgf= 10N(nearly).
It is not constant for a body, but it changes from place to place.
It is measured by a spring balance.

Question 22.
Which quantity : mass or weight, does not change by change of place ?
Answer:
The mass of a body is constant and it does not change by changing the position of the body.

Question 23.
State which of the quantities, mass or weight is always directed vertically downwards.
Answer:
Mass is the quantity of matter contained in a body. Weight is the force with which the earth attracts the body. Weight is always directed vertically downwards.

C. Numericals

Question 1.
A car covers a distance of 160 km between two cities in 4 h. What is the average speed of the car ?
Answer:
Distance =160 km
Time taken = 4h
Speed = ?
Speed = Distance covered / Time taken
= 160km / 4h = 40 km h^-1

Question 2.
A train travels a distance of 300 km with an average speed of 60 km h_1. How much time does it take to cover the distance?
Answer:
Speed = 60 km h^-1
Distance covered = 300 km
Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 8

Question 3.
A boy travels with an average speed of 10 m s^-1 for 20 min. How much distance does he travel ?
Answer:
Average speed of boy = 10 m s^-1
Time taken = 20 min
Distance travelled = Speed × Time taken
Convert minutes into seconds
1 minute = 60 sec.
20 minutes = 20 × 60 = 1200 sec.
Distance travelled = 10 m s^-1 × 1200 sec.
= 12000 m Or 12 km

Question 4.
A boy walks a distance 30 m in 1 minute and another 30 m in 1.5 minute. Describe the type of motion of the boy and find his average speed in m s-1.
Answer:
As the speed does not remain constant throughout the journey the motion is non-uniform
Total distance travelled in going and coming back
d = 30 m + 30 m = 60 m
Total time taken in going and coming back

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 9

Question 5.
A cyclist travels a distance of 1 km in the first hour, 0.5 km in the second hour and 0.3 km in the third hour. Find the average speed of the cyclist in
(i) km h^-1, (ii) m s^-1.
Answer:
(a) Distance travelled in first hour = 1 km
Distance travelled in second hour = 0.5 km
Distance travelled in third hour = 0.3 km
Total time taken = 3 hr
Total distance travelled = 1 + 0.5 + 0.3 = 1.8 km
(i) Average speed in km h^-1

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 10
Average speed in m s^-1
1 km = 1000 m
1.8 km = 1.8 × 1000 m
= 1800 m
1 hour = 3600 seconds
3 hour = 3600 × 3 = 10800 sec.

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 11

Question 6.
A car travels with speed 30 km h^-1 for 30 minute and then with speed 40 km h^-1 for one hour. Find :
(a) the total distance travelled by the car
(b) the total time of travel, and
(c) the average speed of car
Answer:
Speed of car for first 30 minutes = 30 km h^-1
Speed of car for next 1 hour = 40 km h^-1
(a) Total distance travelled by the car

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 12

Question 7.
On earth the weight of a body of mass 1.0 kg is 10 N. What will be the weight of a boy of mass 37 kg in (a) kgf (b) N ?
Answer:
Weight of a body of mass 1.0 kg body = 10 N
(a) Weight of a boy of mass = 37 kg
(b) Weight of a boy of 37 kg in newton will be 1 kgf = 10N
∴ 37 kgf = 37 × 10 N
= 370 N

Question 8.
The weight of a body of mass 6.0 kg on moon is 10 N. If a boy of mass 30 kg goes from earth to the moon surface, what will be his (a) mass, (b) weight ?
Answer:
(a) Mass remains same it does not change
So mass of boy 30 kg on earth = 30 kg on moon surface
(b) Weight of boy on moon becomes 1 / 6
∴ 30 kg boy will weight 30 x 1/6 = 5kg
1 kg = 10 N ⇒ 5 × 10 N = 50 N
∴ Weight of boy on moon surface = 50 N

Selina Concise Physics Class 7 ICSE Solutions – Heat

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Physics Class 7 ICSE Solutions – Heat

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

Selina Class 7 Physics ICSE Solutions Chemistry Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 7 Physics Chapter 5 Heat

Points to Remember
Heat is a form of energy that leads to the sensations of hotness or coldness.
Temperature is the degree of hotness and coldness of a body.
Thermometer is used to measure temperature.
The S.I. unit of temperature is °C.
The most common liquid for a thermometer is mercury.
The main sources of heat are (i) Fire (ii) Sun (iii) Electricity.
Those substances which can easily catch fire are called inflammable substances.
Those substances which are fire resistant are called non-inflammable substances.
The fixed temperature at which freezing of liquid occurs is known as freezing point.
The temperature at which vapourisation occurs is known as the boiling point.
Substances through which heat is easily conducted are called good conductors e.g. silver, gold, copper etc.
Substances through which heat is not easily conducted are called Insultors.
Radiation is the process of transfer of heat from a hot body to a cold body without affecting the intermediate medium.

Test Yourself

A. Objective Questions

1. Write true or false for each statement

(a) On touching a lump of ice, we feel cold because some heat passes from our body to the ice.
Answer. True.

(b) Heat flows from a body at a high temperature to a body at a low temperature when they are kept in contact. .
Answer. True.

(c) All solids expand by the same amount when heated to the same rise in temperature.
Answer. False.

(d) Telephone wires are kept tight between the two poles in summer.
Answer. False.

(e) Equal volumes of different liquids expand by different amounts when they are heated to the same rise in temperature.
Answer. True.

(f) Solids expand the least and gases expand the most on being heated.
Answer. True.

(g) A mercury thermometer makes use of the property of expansion of liquids on heating.
Answer. True.

(h) Kerosene contracts on heating.
Answer. False.

(i) Water is a bad conductor of heat.
Answer. True.

(j) Medium is necessary for the transfer of heat by radiation.
Answer. False.

(k) Land and sea breezes are convection currents of cold and warm air.
Answer. True.

(l) Liquids are heated by conduction and radiation.
Answer. False.

(m) Black surfaces are the poor absorbers of heat radiations.
Answer. False.

2. Fill in the blanks

(a) Heat is a form of energy.
(b) Temperature determines the degree of hotness or coldness of a body.
(c) On heating a body, its temperature rises.
(d) We use a thermometer for measuring the temperature of a body.
(e) The S.I. unit of temperature is kelvin.
(f) In a thermometer, the commonly used liquid is mercury.
(g) The temperature of a normal human body is 37 °C.
(h) A person is said to have fever if his body temperature is more than 98.6
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow from metallic piece to water.
(j) The temperature of boiling water is 100°C.
(k) Liquids expand more than the solids.
(l) Gases expand more than the liquids.
(m) Heat transfer in solids is by conduction.
(n) Heat transfer in liquids and gases is by convection.
(o)Metals are conductors of heat.
(p) Still air is an insulator of heat.
(q) Black and dull surfaces are good absorbers of heat.

3. Match the following

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 1

4. Select the correct alternative

(a) If we add a lump of ice to a tumbler containing water,

heat flows from water to ice
heat flows from ice to water
heat flows from water to ice if water is more
heat flows from ice to water if ice is more

(b) The temperature of pure melting ice is

0°C
100°C
95°C
98.6°F

(c) A thermometer uses

water
mercury
air
none of the above

(d) Which of the statement is correct

Iron rims are cooled before they are placed on cart wheels
A glass stopper gets tight on warming the neck of the bottle
Telephone wires sag in winter, but become tight in summer
A little space is left between two rails on a railway track

(e) Heat in a liquid is transferred by

conduction
convection
radiation
conduction and radiation

(f) In the process of convection, heat travels

sideways
downwards
upwards
in all directions

(g) The vacuum kept in between the walls of a thermos flask reduces the heat transfer by

conduction only
convection only
radiation only
conduction and convection

B. Short/Long Answer Questions

Question 1.
What is heat ? State its S.I. unit.
Answer:
Heat is a form of energy which flows. It is the energy of motion of molecules constituting the body.
The unit of heat is same as that of energy, The S.I. unit of heat is joule (abbreviated as J) and other common units of heat are calorie and kilo calorie, where 1 k cal = 1000 cal.

Question 2.
What is meant by the term temperature.
Answer:
Temperature is a quantity which tells the thermal state of a body (i.e. the degree of hotness or coldness). It determines the direction of flow of heat when the two bodies at different temperatures are placed in contact.

Question 3.
State the three units of temperature.
Answer:
The S.I. unit of temperature is kelvin or K. The other most common unit of temperature is degree Celsius (°C) and degree Fahrenheit (°F).

Question 4.
Name the instrument used to measure the temperature of a body.
Answer:
To measure the temperature of a body with the help of a thermometer.

Question 5.
Name two scales of temperature. How are they inter-related?
Answer:
Two scales of temperature are
(i) Celsius (ii) Fahrenheit
Relation:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 2

Question 6.
How is the size of a degree defined on a Celsius scale ?
Answer:
The interval between the ice point and steam point divided by 100 (hundred) equal parts is called a degree on the Celsius scale.

Question 7.
How is the size of a degree defined on a Fahrenheit scale?
Answer:
The interval between the ice point and steam point divided into 180 equal parts is called a degree on the Fahrenheit scale.

Question 8.
State the temperature of (i) ice point and (ii) steam point, on the Celsius scale.
Answer:
(i) Ice point. Is the the mark on Celsius scale at which ice melts. Ice point on the Celsius scale is 0°C.
(ii) Steam point. On the Celsius scale is the mark at which water changes into steam at normal atmospheric pressure. On Celsius scale it is 100°C.

Question 9.
Write down the temperature of (i) lower fixed point, and (ii) upper fixed point, on the Fahrenheit scale.
Answer:
Lower fixed point: On the Falirenheit scale is the mark at which pure ice melts. It is 32°F on Fahrenheit scale.
Upper fixed point: On the Fahrenheit scale is the mark at which water starts changing into steam at normal atmospheric pressure. It is 212°F.

Question 10.
What is the Celsius scale of temperature ?
Answer:
Celsius scale is that which has ice point as 0°C and steam point marked as 100°C.

Question 11.
What is the Fahrenheit scale of temperature ?
Answer:
Fahrenheit scale is that which has ice point as 32°F and the steam point marked as 100°C.

Question 12.
What is the Kelvin scale of temperature ?
Answer:
On Kelvin scale of temperature zero mark is when no molecular motion occurs. Ice point is at 273 and steam point is at 373 K. Thus 0 K = – 273°C and one degree on Kelvin scale is same as one degree on Celsius scale.

Question 13.
The fig. shows a glass tumbler containing hot milk which is placed in a tub of cold water. State the direction in which heat will flow.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 3
Answer:
When we bring two objects of different temperature together, energy will always be transferred from hotter to the cooler object.
Here, also heat will flow from hot milk tumbler to tub of cold water.

Question 14.
Draw a neat labelled diagram of a laboratory thermometer.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 4

Question 15.
Write down the body temperature of a healthy person.
Answer:
The temperature of a healthy persons is 98.6 degrees fahrenheit or 37.0 degree Celsius or 310 k.

Question 16.
What do you understand by thermal expansion of a substance ?
Answer:
The expansion of a substance when, heated, is called thermal expansion.
Or
Thermal expansion is the tendency of matter to change .in shape, area and volume in response to a change in temperature.

Question 17.
Name two substances which expand on heating.
Answer:
Mercury and Aluminium wire.

Question 18.
Why do telephone wires sag in summer ?
Answer:
The telephone wires will sag in summer due to expansions and will break in winter due to contraction.
Therefore, while putting up the wires between the poles, care is taken that in summer they are kept slightly loose so that they may not break in winter due to contraction.
While in winter they are kept light so that they may not sag too much in summer due to expansion.

Question 19.
Iron rims are heated before they are fixed on the wooden wheels. Explain the reason.
Answer:
The wooden wheels of a bullock-cart are fitted with iron tyres. To ensure a tight fit, the tyre is made slightly smaller in diameter than the wheel. The tyre is first heated due to which it expands. The heated tyre is then fitted on the wheel. When the tyre cools, it contracts and makes a tight fit on the wheel.

Question 20.
Why are gaps left between successive rails on a railway track ?
Answer:
The rails of railway track are made of steel. While laying the railway track, a small gap is left between the two successive length of rails. The reason is that the rails expand in summer. The gap is provided to allow for this expansion. If no gap is left, the expansion in summer will cause the rails to bend sideways. This may result in a train accidents.

Question 21.
A glass stopper stuck in the neck of a bottle can be removed by pouring hot water on the neck of the bottle. Explain why ?
Answer:
When hot water is poured over the neck of the bottle, it expands. As a result the stopper gets loosened and can be removed easily.

Question 22.
Why is a cement floor laid in small pieces with gaps in between?
Answer:
The floor is laid in small pieces with gaps in between to allow for the expansion during summer. However glass strips can be placed in the gaps.

Question 23.
One end of a steel girder in a bridge is not fixed, but is kept on roliers. Give the reason.
Answer:
In the construction of a bridge, steel girders are used. One end of the girder is fixed into the concrete or brick pillars and its other end is not fixed, but it is placed on rollers. The reason is that if there is any rise (or fall) in temperature of atmosphere, the girder can freely expand (or contract) without affecting the pillars.

Question 24.
Describe one experiment to show that liquids expand on heating.
Answer:
(i) Take an empty bottle with a tight fitting cork having a hole drilled in its middle, a drinking straw, two bricks, a wire guaze and a burner.
(ii) Fill the bottle completely with water and add few drops of ink in it to make it coloured.
(iii) Fix the cork in the mouth of the bottle and pass the drinking straw through the cork. Put some molten wax around the hole so as to avoid the leakage of water.
(iv) Pour some more water into the drinking straw so that water level in the straw can be seen. Mark the water level in the straw as shown in Figure.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 5
(v) Place the bottle on the wire gauze kept over the two bricks as shown in Figure. Then heat the bottle by means of a burner.
(vi) Look at the level of water in the straw.
You will notice that as the water is heated more and more, the level of water in the drinking straw rises. This shows that water expands on heating.

Question 25.
State one application of thermal expansion of liquids.
Answer:
Mercury is a metal found in liquid state. It expands more and uniformly over a wide range of temperature. So mercury is used as thermometric liquid.

Question 26.
Describe an experiment to show that air expands on heating.
Answer:
(i) Take an empty bottle. Actually the empty bottle contains air. Attach a rubber balloon to its neck as shown in Figure. Initially, the balloon is deflated.
(ii) Place the bottle in a water bath containing boiling water. After some time you will notice that the balloon gets inflated as shown in Figure. The reason is that the air inside the bottle expands on heating and it fills the balloon.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 6
(iii) Take the bottle out of the water bath and 7 allow it to cool by itself. We will notice that the balloon gets deflated and it collapses. This is because the air inside the balloon and the bottle, has contracted on cooling. The air from balloon passes to the bottle, so the balloon gets deflated.

Question 27.
An empty glass bottle is fitted with a narrow tube at its mouth. The open end of the tube is kept in a beaker containing water. When the bottle is heated, bubbles of air are seen escaping into the water. Explain the reason.
Answer:
When the bottle is heated, bubbles of air are seen escaping into the water. This happens because the air present in glass bottle expands on heating and tries to escape out through the tube into the water.

Question 28.
State which expands more, when heated to the same temperature : solid, liquid or gas ?
Answer:
Gases expand much more than the liquids and the solids. Like liquids, the gases do not have a definite shape, so they also have only the cubical expansion.

Question 29.
Name the three modes of transfer of heat.
Answer:
There are three modes of transfer of heat (i) Conduction (ii) Convection (iii) Radiation.
(i) Conduction “is that mode of transfer of heat, when heat travels from hot end to cold end from particle to particle of the medium, without actual movement of particles.”
(ii) Convection. “Is a process of transfer of heat by actual move-ment of the medium particles.”
(iii) Radiation. “Is that mode of transfer of heat in which heat directly passes from one body to the other body without heating the medium.”

Question 30.
Name the mode of transfer of heat in the following :
(a) solid,
(b) liquid,
(c) gas
(d) vacuum
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 7

Question 31.
What are the good and bad conductors of heat ? Give two examples of each.
Answer:
Good conductors. “The substances through which heat is easily conducted are called good conductors of heat.”
Example : Copper, iron.
Bad conductors. “The substances through which heat is not conducted easily are called bad conductors of heat or poor conductors of heat.”
Example : Wood, cloth.

Question 32.
Name a liquid which is a good conductor of heat.
Answer:
Mercury is good conductor of heat.

Question 33.
Name a solid which is a good conductor of heat.
Answer:
Aluminium is a good conductor of heat.

Question 34.
Select good and bad conductors of heat from the following :
copper, mercury, wood, iron, air, saw-dust, cardboard, silver, plastic, wool.
Answer:
Good conductors — Mercury, copper, silver, iron.
Bad conductors — Wood, air, saw dust, plastic, wool, cardboard.

Question 35.
Why is an oven made of double walls with the space in between filled with cork ?
Answer:
An oven is made of double walls and the space between them is filled with wool, cork etc. because the wool and cork are the insulator of heat. They prevent the heat of the oven to escape.

Question 36.
Why do we use cooking utensils made up of copper.
Answer:
Cooking utensils are made of metals such as copper, aluminium, brass, steel etc., so that heat is easily conducted through the base to their contents. But they are provided with handles of bad conductors (such as ebonite or wood) to hold them easily as handles will not conduct heat from the utensil to our hand.

Question 37.
Why is a tea kettle provided with an ebonite handle ?
Answer:
Tea kettles are provided with wooden or ebonite handles. The wood or the ebonite being the insulators of heat, does not pass heat from the utensils to our hand. Thus, we can hold the hot utensils or pans comfortably by their handles.

Question 38.
In summer, ice is kept wrapped in a gunny bag. Explain the reason.
Answer:
In summer, the ice is kept wrapped in a gunny bag or it is covered with saw dust. The air filled in the fine pores of the gunny bag or saw dust, is the insulator of heat. The air does not allow heat from outside to pass through it to the ice. Thus, the ice is prevented from melting rapidly.

Question 39.
Explain why
(a) we wear woolen clothes in winter.
(b) the water pipes are covered with cotton during very cold weather.
Answer:
(a) Woolen clothes have fine pores filled with air. Wool and air both are bad conductors of heat. Therefore in winter, we wear woolen clothes as they check the conduction of heat from the body to the surroundings and thus keeps the body warm.
(b) During very cold weather, the water pipes are covered with cotton. The cotton has air trapped in its fine pores. The cotton and air are the insulators of heat. They do not pass heat from water inside the pipes to the outside atmosphere. Thus, cotton prevents the water in the pipes from freezing.

Question 40.
Why are quilts filled with fluffy cotton ?
Answer:
Quilts are filled with fluffy cotton. Air is trapped in the fine pores of cotton. Cotton and air are the insulators of heat. They check heat from our body to escape and thus keep us warm.
The newly made quilts are warmer than the old ones because in the old quilts, there is no air trapped in the cotton.

Question 41.
State the direction of heat transfer by way of convection.
Answer:
By the process of convection, heat is always transferred vertically upwards. The reason is that the medium particles near the source of heat absorb heat from the source and they start moving faster. As a result, the medium at this place becomes less dense so it rises up and the medium from above being denser, moves down to take its place. Thus, current is set up in the medium which is called a convection current. The current continues till the entire medium acquires the same temperature.

Question 42.
Why is a ventilator provided in a room ?
Answer:
Ventilators and windows are provided in rooms for proper ventilation. The reason is that when we breathe out in a room, the air in the room becomes warm and impure. The warm air is less dense i.e. lighter, so it rises up and moves out through the ventilators. Then the cold fresh air comes in the room through the windows to take its place. Thus the continuous circulation of fresh air keeps the air in the room fresh.

Question 43.
Why are chimneys provided over furnace in factories ?
Answer:
Chimneys are provided over the furnace in factories. This is because the hot gases coming out of the furnace are less dense than the air. They rise up through the chimney. The smoke, fumes etc. around the furnace rush in so as to take their place and they are sucked out. Thus, the chimney helps to remove the undesired fumes, smoke etc. from the premises.

Question 44.
What are the land and sea breezes ? Explain their formation.
Answer:
LAND BREEZE : Blowing of breeze (air) from land towards sea is called land breeze.
During night land and sea water both lose heat. Specific heat capacity of land being very low as compared to that of sea water, land loses heat energy fast and cools more rapidly as compared to sea. Sea water being at higher temperature, the air above it becomes lighter and rise up. Air from land being at higher pressure. So air from land starts blowing towards sea and gives rise to Land Breeze.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 8
SEA BREEZE : Blowing of breeze (cold air) from sea towards land during the day is called the SEA BREEZE. During day time land and sea both are heated equally by the sun, but land has very low specific heat capacity as compared to sea, is heated up more quickly. Thus air above land due to heat becomes lighter and rises up. Thus pressure decreases and cold and humid air above the sea starts blowing towards land, thereby giving rise to SEABREEZE.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 9

Question 45.
Why is the freezing chest in a refrigerator fitted near its top?
Answer:
Freezing chest in a refrigerator is fitted near the top, because it cools the remaining space of the refrigerator by convection current. Air near the top comes in contact with the freezing chest gets cooled, becomes denser and therefore descends while the hot air from the lower part rises and hence convection currents produced cool the whole space inside.

Question 46.
Explain briefly the process of heat transfer by radiation.
Answer:
RADIATION. “The transfer of heat energy from a hot body to cold body directly, without heating the medium between two bodies is called RADIATION.”
The radiant heat or thermal radiation is of the form of ELECTROMAGNETIC WAVES. These waves can travel even in vacuum in all directions in straight line with the speed of light. They do not heat the medium through which they pass. Heat radiations are also called INFRA-RED RADIATIONS because the wavelength of heat radiations is longer than that of visible light. These radiations can cause heating effect only if they are absorbed by some material.

Question 47.
Give one example of heat transfer by radiation.
Answer:
When we sit in the sun, we feel warm. We cannot get heat from the sun by the process of conduction or convection because most of the space between the sun and the earth is a vacuum and both of these modes of heat transfer require medium. Hence, one must be getting heat from the sun by the mode of radiation.

Question 48.
Why do we prefer to wear white or light coloured clothes in summer and black or dark coloured clothes in winter ?
Answer:
We prefer to wear white clothes in summer. The reason is that the white clothes reflects most of the sun’s heat and absorb very little of the sun’s heat, thus they keep our body cool.
We prefer to wear black and dark coloured clothes in winter. The reason is that the black or dark colour clothes absorb most of the sun’s heat and keep our body warm.

Question 49.
The bottom of a cooking utensil is painted black. Give the reason.
Answer:
The bottom part of the cooking utensil or pan is painted black. The reason is that the black surface absorbs more heat and so the contents of utensil or pan get cooked rapidly if its bottom part is painted black.

Question 50.
Draw a labelled diagram of a thermo flask. Explain how the transfer of heat by conduction, convection and radiation is reduced to a minimum in it.
Answer:
Heat transfer is minimised because of:
(1) The vacuum between the two walls, rubber, glass, cork and air do not allow the loss of heat by conduction.
(2) Cork in the neck of flask and the cup over it prevent loss of heat by convection.
(3) Heat cannot be lost by conduction or convection because of vacuum between the two walls.
(4) Heat loss is also minimised by radiation, by making outer surface of inner wall and inner surface of outer wall silvered. The inner wall is a BAD RADIATOR and the outer wall is a GOOD REFLECTOR of radiation.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 10

C. Numericals

Question 1.
The temperature of a body rises by 1°C. What is the corresponding rise on the (a) Fahrenheit scale (b) Kelvin scale?
Answer:
(a) Since 100 divisions on Celsius scale =180 divisions on the Fahrenheit scale 1 division on Celsius scale
∴ 1 division on Celsius scale
= 1.80 / 1.00 × 1
= 1.8 divisions in the Fahrenheit scale.
For 1°C rise corresponding rise in Fahrenheit = 1.8°F
(b) Since 100 divisions in the Celsius scale = 100 divisions in the Kelvin scale
1 division on Celsius scale = 100 / 100 × 1
= 1 division on Kelvin scale
For 1°C rise corresponding rise in Kelvin is 1 K.

Question 2.
The temperature rises by 18°F. What is the rise on the Celsius scale ?
Answer:
Since 100 divisions on the Celsius scale =180 divisions on the Fahrenheit scale
∴ 18 divisions on Fahrenheit scale.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 11

Question 3.
Convert 5°F to the Celsius scale.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 12

Question 4.
Convert 40°C to the (a) Fahrenheit scale (b) Kelvin Scale.
Answer:
(a) Fahrenheit scale
C = 40°C
Substitute value of C = 40° in below equation

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 13

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 14

Question 5.
Convert – 40°F to the Celsius scale.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 15

Selina Concise Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

August 11, 2022December 5, 2019 by Prasanna

Selina Concise Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Chemistry for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Chemistry ICSE Solutions Physics Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 7 Chemistry Chapter 2 Physical and Chemical Changes

Points to Remember :

All changes are classified into two types
(i) Physical change
(ii) Chemical change.
Physical Change— A physical change is a temporary change in which no new substance is formed and chemical composition remains same. e.g. Melting of ice.
Chemical Change— A chemical change is a permanent change, in which a new substances are formed whose chemical composition and physical properties are different, e.g. Burning of a candle.
Chemical Reaction— Any chemical change in matter involving its transformation into one or more new substances is called a chemical reaction.
Chemical Equations— A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formulae of the substances involved in the reaction.
The substances that react with one another are called reactants, and the new substances thus formed are called products.
A balanced chemical reaction is one in which the number of the atoms of each element on the
reactant side is equal to the number of atoms of that element on the product side.
The law of conservation of mass states that mass can neither be created nor be destroyed.
A chemical equation gives both qualitative and quantitative information about reactants aftd products.
The type of chemical reaction in which two substances combine to form a new substance is known as combination reaction.
The type of chemical reaction in which a substance breaks up on heating to form two or more simpler substances,
which can be either elements or compounds, known as decomposition reaction.

Exercise

Question 1.
(a) Define:
(i) a physical change
(ii) a chemical change
(b) Give two examples for each of the above two changes.
Answer:
(a) (i) Physical chagne : A temporary change in which no new substance is formed, the composition of substance remains the same, though its state, shape and size may change.
(ii) Chemical change : A permanent change in which new substances are formed whose composition and properties are completely different from those of the original substances.
(b) Physical change:
(i) Change of water into its vapours.
(ii) Heating of iron rod.
Chemical change:
(i) Burning of wood.
(ii) Breathing.

Question 2.
What are reversible and irreversible changes ? Give one example for each.
Answer:

Reversible change : When a change in a substance can be reversed by changing the conditions, it is said to be a reversible change.
Example : Melting of ghee or wax.
Irreversible change : When a substance can not be brought back to its original state after a change, it is said to be an irreversible change.
Example : Souring of milk.

Question 3.
Mention a change which is always
Answer:

Desirable : Changes that are useful to man are desirable changes, e.g. change of milk into curd.
Undesirable : Change that brings about destruction is an undesirable change, e.g. floods and epidemics are undesirable changes.
Periodic : Changes that are repeated at regular intervals of time are called periodic changes, e.g. change of day and night.

Question 4.
Is burning a physical change or a chemical change? Why?
Answer:
Burning is a chemical change as new substance is formed with new properties and it cannot be reversed.

Question 5.
A burning candle shows both physical and chemical changes. Explain ?
Answer:
A burning candle produces wax vapours which solidify and form wax again is physical change. At the same time wax on burning produces water vapours and carbondioxide which escape into the atmosphere which are new substances with new properties. It is a chemical change.
Hence burning of candle shows both physical and chemcial changes.

Question 6.
State three differences between evaporation and boiling
Answer:

Evaporation	Boiling
Evaporation is a slow process. Evaporation takes place from the surface of the liquid. Evaporation takes place at all temperature.	Boiling is a fast process. Bgiling takes place from all parts of the liquid. Boiling takes place at a fixed temperature on heating.

Question 7.
State four differences between physical and chemical changes.
Answer:
Four differences are :

Physical change	Chemical change
No new substances with new properties are formed. It can be reversed by simple physical methods. It is temporary change. Energy is neither needed nor produced.	New substances with new properties are formed. Change cannot be reversed by simple physical methods. It is permanent change. Energy is either needed or evolved.

Question 8.
What do you observe when :

water is boiled
On boiling water changes into steam (gas) physical change.
a piece of paper is burnt
On burning piece of paper produces carbon dioxide and ash is left behind. Is a chemical change.
some ice cubes are kept in a glass tumbler
Ice cubes (solid) turn into water (liquid) only state changes (physical change).
solid ammonium chloride is heated
Solid ammonium chloride on heating changes into vapours (change of state) is physical change.
an iron nail is kept in tap water for few days
We observe reddish brown coating on the nail called rust (entirely new substance) is chemical change.
a spoon of sugar is heated in a pan
When a spoon of sugar is heated in a pan, black (charred sugar) (carbon) is seen. Is a chemical change.
lighted match stick is brought near the mouth of the test tube containing hydrogen gas.
We observe that hydrogen bums at the mouth of test tube with blue flame and pop sound is heard. It is chemical change.
quick lime is dissolved in water.
The following two observations will be observed
(i) A hissing sound is observed.
(ii) The mixture starts boiling and lime water is obtained.
liittle ammount of curd is added to a bowl containing warm milk and kept for five hours.
When a little amount curd is added to a bowl containing warm milk and kept for five hours, a permanent change occured.
The milk will change to curd. On boiling water changes into steam (gas) physical change.

Question 9.
Name a chemical change which takes place in presence of:
Answer:
Heat:

Burning of paper.
Cooking of food need heat.

Light :

Formation of food by plants i.e. photosynthesis need light.
Hydrogen and chlorine react in presence of light

Electricity:

Water breaks into hydrogen and oxygen on passing electricity.
Sodium chloride solution breaks up into its components sodium and Chlorine on passing electric current through sodium chloride solution.

Objective Type Questions

Question 1.
Fill in the blanks.

A new substance is always formed in a chemical change.
Melting of ice is a physical change.
When a candle burns, wax melts. Melting of wax is a physical change.
Chemical change occurs as a result of rearrangement of atoms between two substances.
Burning of a fuel is a chemical change.
Revolution of the earth around the sun is a natural periodic change.
Growing of a seedling into a plant is chemical change.

Question 2.
State whether the following are physical or chemical changes.

glowing of a bulb — physical change,
burning of sugar — chemical change,
heating of water — physical change,
growing of a piglet into a pig — chemical change,
burning of wood — chemical change,
passing electric current through a heater rod — physical change.
water cycle in nature — physical change,
respiration in living beings — chemical change,
shaping a piece of glass — physical change,
lightning — chemical change,
(energy produced) dissolving sugar in water — physical change,
heating a mixture of iron filings and sulphur—chemical change.
mixing oil with water — physical change.
cutting wood into small pieces — physical change,
photosynthesis — chemical change.
Digestion of food — chemical change.
Melting of wax — physical change.
Boiling of an egg — chemical change.
Slaking of lime — chemical change.

Question 3.
Match the following:

Physical and Chemical changes 1

Answer:

Question 4.
Write true or false against the following statements :

Cutting of paper into pieces is a chemical change.
False
Rusting of iron is a chemical change.
True
Earthquake is a desirable change.
False
Melting of ice is a physical change.
True
Burning of sugar is a temporary change.
False

Multiple Choice Questions

Tick (√) the correct alternative from the choice given for the following statements :
Question 1.
A substance which can not sublime is
Answer:

iodine
camphor
sugar
dry ice

Question 2.
When you put some ice cubes in a glass, droplets of water are formed on the outerwall of the glass. This explains the phenomenon of
Answer:

melting
freezing
condensation
evaporation

Question 3.
Burning is a
Answer:

slow process
fast process
natural process
none of the above

Question 4.
Which one of the following is volatile in nature ?
Answer:

common salt
petrol
water
milk

Question 5.
An example of both physical and chemical change is
Answer:

burning of candle
melting of ice
cooking of food
blowing of bulb

Question 6.
The compound rust is a hydrated oxide of
Answer:

copper
aluminium
iron
gold

Question 7.
When sugar is heated, its colour changes into
Answer:

red
brown
black
grey

Question 8.
A pop sound is heard when a lighted match stick is brought
near the mouth of a jar. This indicates the release of gas.
Answer:

oxygen
hydrogen
nitrogen
water-vapour

Question 9.
When we add water to the following substances, which one will show a chemical change ?
Answer:

salt
sugar
oild
quick lime

Selina Concise Biology Class 8 ICSE Solutions – Ecosystems

August 11, 2022December 5, 2019 by Veerendra

Selina Concise Biology Class 8 ICSE Solutions – Ecosystems

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 4 Ecosystems. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE Solutions Chemistry Physics Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 4 Ecosystems

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

a. The term “ecosystem” is derived from the Greek word “Oikos” meaning.

Body weight
Food
House
Size

b. Rat in any food chain would occupy the position of

Tertiary consumer
Secondary consumer
Primary consumer
Producer

c. Evergreen broad-leaved trees are characteristic of

Tropical rain forests
Temperate deciduous forests
Coniferous forests
All of the above types of forests.

Short Answer Type:

1. Mention if the following statements are true (T) or false (F).
(a) Snakes are primary consumers (T/F)
(b) Some humans are strictly primary consumers & some others are of other types of consumers also (T/F)
(c) No ecosystem can survive without light (T/F)
(d) Cattle go to ponds for drinking water, so they are a constituent of pond ecosystem (T/F)

Answer:

(a) Snakes are primary consumers (F)
No the snakes are not primary consumers as snakes eat rats and frogs as these are primary consumers which eat plant products. As snakes eat the primary consumers so the snakes are secondary consumers.

(b) Some humans are strictly primary consumers and some others are of other types of consumers also (T)
It is true that humans are vegetarians and eat plants or plant products. So these humans are vegetariBut there are certain humans which eat the flesh or eggs of other animals. These are carnivores and humans living plants are called Herbivores.

(c) No ecosystem can survive without light (T)
The plants and animals and micro-organisms present at a place and interacting with the atmosphere like sun light, air, water, soil and warmth and dwelling at a place like, pond, desert, forest, rock form the ecosystem as pond ecosystem, desert ecosystem forest ecosystem. So ecosystem cannot survive without the presence of light. As the flora (plants) living in that ecosystem can only make food in the presence of light and the animals (Fauna) living in that ecosystem get the food from the plants of that ecosystem. So flora in that area cannot survive in that area without light and animals living in that area will not get the food and the plants and animals will perish and the ecosystem cannot survive.

(d) Cattle go to ponds for drinking water, so they are a constituent of pond ecosystem (F)
Cattles likes tigers, lions, cows, deers, buffaloes, go to take water from the pond and return to their dwellings as tigers, deers etc. come to the forest so they form a forest ecosystem. But plants like hydrilla, vallineria, lotus etc. and animals like frogs, beetles, fish live in the pond and form the pond ecosystem. But animals like buffalo which come only to take~water cannot form a part of the pond ecosystem.

2. Match the items in Column I with as many items as possible in Column II.

Selina Concise Biology Class 8 ICSE Solutions – Ecosystems 2
Answer:

Selina Concise Biology Class 8 ICSE Solutions – Ecosystems 3
3. Rewrite the following in their correct sequence in a food chain:
(a) Snake → Grasshopper → Grass → Frog
(b) Grass → Tiger → Deer
(c) Snake → Peacock → Rat → Wheat

Answer:

(a) Grass → Grasshopper → Frog → Snake
(b) Grass → Deer → Tiger
(c) Wheat → Rat → Snake → Peacock

Long Answer Type:

Question 1.
Differentiate among primary, secondary and tertiary consumers. Give one example of each in a food chain.
Answer:
All plants produce food through photosynthesis and are categorised as self food producers i.e. these are autotrophs. There are plant eating animals called herbivores as Rabbits, deers, pigeons, cows, buffaloes etc. and insects like grasshoppers, bees, butterflies and crickets also eat plants or plant products as fruits, flowers, pollen grains and plant juices. Such animals are called primary consumers.
Animals like tigers, lions, wolves, lizards, frogs eat the primary consumers. Birds vultures, kites, eagles eat the primary consumer, (i.e. These birds are well eat the flesh of many birds like pigeons, sparrows.) These animals or birds are called secondary consumers.
Animals like snakes are eaten by the peacocks, they eat the secondary consumers and are called tertiary consumers.
Owls, eagle are top carnivore. So it is quaternary consumer.

Question 2.
Define the term (a) flora and (b) fauna.
Answer:
Flora: Plants occurring in a particular is called flora of that area i.e. vegetative growth forms flora. Flora deals with plants.
Fauna: The animals occurring in a area form the fauna of that area. Fauna deals with animals.
Flora and fauna of an area is the plants and animals found in that area.

Question 3.
List any three members each of the flora and fauna of tropical rain forests.
Answer:
Tropical rain forest are on western coast of India and in the north, east.
Flora: bamboos, ferns, shrubs (Evergreen trees).
Fauna: leopards, jungle cats, monkeys, snakes, flying squirrels, insects, snails, centipedes, millipedes.

Question 4.
Define the following terms and give two examples in each case.
(a) Symbiosis
(b) Parasitism
(c) Predation
Answer:
(a) Symbiosis: It refers to relationships between organisms of different species that show on intimate association with each other. Symbiotic relationships provide atleast one of the participating species with a nutritional advantage.
Examples of Symbiosis Relationships are of Fungus and photosynthestic alga and Microbes and cattle.

(b) Parasitism: Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Examples of Parasitism are 4 tapeworms, flukes, the plasmodium species and mosquitoes.

(c) Predation: A predator is any consumer that kills and eats another living organism in order to obtain energy. The organism being eaten is called the prey.
Examples are Lions, Deer, Wolves, Eagles.

Selina Concise Biology Class 7 ICSE Solutions – Photosynthesis and Respiration

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Biology Class 7 ICSE Solutions – Photosynthesis and Respiration

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

Selina Class 7 Biology ICSE Solutions Chemistry Physics Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 7 Biology Chapter 4 Photosynthesis and Respiration

Synopsis —

The process of preparing or synthesising food using water from the soil and carbon dioxide from the air, together chlorophyll and sunlight is called photosynthesis.
Photosynthesis occurs in the mesophyll cells of the leaf. These cells contain numerous plastids called chloroplasts.
With in the plastids is present the green pigment called chlorophyll.
On the lower surface of the leaf are numerous pores called stomata, which open into small air cavities inside the leaf.
Stomata are tiny openings found mainly on the lower surface of leaves. These openings are surrounded by a pair of bean¬shaped cells called guard cells.
All plants have a transport system called vascular system. It is composed of two types of tissues called xylem and phloem.
There are two end-products of photosynthesis :
- Glucose (C₆H₁₂O₆)
- Oxygen
The energy released during respiration is stored as chemical energy in the form of ATP — adenosine tri-phosphate.
Aerobic respiration —
C₆H₁₂O₆+6O_{2 →}6CO₂+6H₂O+38ATP
Anaerobic respiration —
C₆H₁₂O₆ → 2C₂H₅OH+2CO₂+2ATP
During vigorous exercise, the cells respire anaerobically and form lactic acid which accumulate in the muscle cells causing fatigue and pain.
Cellular respiration is called internal respiration which takes place in the cells of living organisms.

The frog respires through
1. skinmouth
2. lining
3. lungs.
The respiratory organs of the fish are gills.
Transpiration is the loss of water in the form of water vapour from the aerial parts of the plant.
Transpiration occurs through stomata.

The factors which affect the rate of transpiration are
1. Sunlight
2. Temperature
3. Wind
4. Humidity

The significance of transpiration
- Maintain the concentration of the sap inside the plant body.
- Causes cooling effect

Review Questions

Multiple Choice Questions
1. Put a tick (✓ ) against the most appropriate alternative in the following statements.
(i) Carbohydrates are stored by plants in the form of:
(a) Vitamins
(b) Proteins
(c) Fats
(d) Glucose

(ii) Stomata are present on the surface of:
(a) Leaves
(b) Roots
(c) Stem
(d) Flower petals

(iii) Which one of the following is an end-product of photosynthesis ?
(a) Fructose
(b) Glucose
(c) Cellulose
(d) Lactose

Short Answer Questions

1. Why do leaves generally look green ?
Answer:
The green colour of a leaf is due to the presence of chlorophyll.

2. Which four of the following are needed for photosyn-thesis in a leaf:
(i) Carbon dioxide:
(ii) Oxygen:
(iii) Nitrates :
(iv) Water:
(v) Chlorophyll:
(vi) Soil:
(vii) Light:
Answer:
(i) Carbon dioxide: from air
(iv) Water: from soil
(v) Chlorophyll: contained in leaf
(vii) Light: from sunlight

3. What is the source of energy for photosynthesis ?
Answer:
Light is the ultimate source of energy in photosynthesis because plants take in the sunlight CO₂ and H₂O and converts it into glucose.

4. Which gas is taken in and which one is given out by the leaf in bright sunlight ?
(i) Taken in :
(ii) Given out:
Answer:
(i) Carbon dioxide
(ii) Oxygen

5. Suppose we compare the leaf with a factory, match the items in Column A with those in Column B.
ColumnA Column B
Selina Concise Biology Class 7 ICSE Solutions - Photosynthesis and Respiration 2

Answer:

6. State whether the following statements are True or False:

(i) Green plants prepare their food by using two raw materials, oxygen and water.
False. Green plants prepare their food by using raw materials, CO, chlorophyll and water.
(ii) The chlorophyll enables the plants to use light energy.
True
(iii) The free oxygen in the atmospheric air is the result of photosynthesis.
True
(iv) Photosynthesis occurs only in chlorophyll-containing parts of the plant.
True

7. Differentiate between aerobic and anaerobic respiration. Write the overall chemical equations of the two kinds of respiration in plants.
(i) Aerobic:
(ii) Anaerobic:
Answer:
Aerobic respiration

It occurs in the presence of oxygen.
Here there is complete breakdown of glucose releasing carbon-di-oxide, energy. water and energy.
More energy is released (38 ATP).

Anaerobic respiration

It occurs in the absence of oxygen.
There is partial breakdown of glucose into ethyl alohol, carbon-di-oxide and
Lesser energy is released (2 ATP).

(i) Aerobic respiration:

(ii) Anaerobic respiration:

Question 8.
Explain how photosynthesis is different from respiration.
Answer:
Photosynthesis

Anabolic process
Food is produced here.
Oxygen is by-product.
Chlorophyll and sunlight are required.
Occur only during daytime.
Occurs in green plants only.

Respiration

Catabolic process
Food is broken down form here to release energy
Carbon-di-oxide is the by-product.
Chlorophyll and sunlight are notrequired.
Occurs all the time
Occurs in all living beings including plants.

Photosynthesis :

Respiration:

C6H12O6+6O→6CO₂+6H₂0+energy

Question 9.
Do the plants respire all day and night or only during the night ?
Answer:
The plants respire only during the night. Plants take in oxygen and give out carbon dioxide. Hence, there is some truth in the belief that one should not sleep under the trees at night.

Question 10.
What happens to the energy liberated during respiration?
Answer:
The energy liberated during respiration is utilised for carrying out various life processes.
Some of the energy liberated during the breakdown of 03 the glucose molecule, is in the form of heat, but a large part of it is converted into chemical energy called Adenosine Triphosphate (ATP). Any activity inside the cell is carried out by the energy released by these ATP molecules.

Long Answer Questions

Question 1.
In order to carry out photosynthesis, what are the substances that a plant must take in ? Also mention their sources.
Answer:
For preparing food, the plants require the following :

Water (from soil)
Carbon dioxide (from air)
Chlorophyll (contained in the leaf)
Energy (from sunlight)

The process of preparing or synthesising food using water from the soil and carbon dioxide from the air, together chlorophyll and sunlight is called photosynthesis. This entire process is a series of complex chemical reactions Photosynthesis is represented as follows:

Question 2.
What is the role of chlorophyll in photosynthesis ?
Answer:
This pigment is of utmost importance as it absorbs the sunlight which provides energy for the process of photosynthesis occurs inside the chloroplast of the leaf.

Question 3.
Do plants need oxygen ? If so, what is its source ?
Answer:
Yes plants need oxygen, all the free oxygen in the atmospheric air is the result of photosynthesis. No animal can survive without oxygen as it is needed for respiration. Even the plants use the same oxygen in dark for their own respiration.

Selina Concise Physics Class 6 ICSE Solutions – Simple Machines

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Physics Class 6 ICSE Solutions – Simple Machines

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Physics ICSE Solutions Chemistry Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 6 Physics Chapter 4 Simple Machines

Synposis
Work is said to be done when a force applied on a body moves it. If the body does not move on applying a force on it, no work is done by the force.
The capacity of doing work is called energy.
A machine is a device which helps us to do work more easily.
A machine enables us to apply a less effort for a load greater than the effort or to apply the effort at convenient point and in a desired direction.
Some machines are simple and some are complex.
The mechanical advantage of a machine is the ratio of the load to the effort, i.e., Mechanical advantage = Load / Effort
Smaller the effort required for a certain load, greater is the mechanical advantage of the machine.
The efficiency of a machine is the ratio of the useful work done on the load by the machine to the work put into the machine by the effort, i.e.
Efficiency = Work output / Work input
The efficiency of an ideal machine is 1 (or 100 per cent).
The efficiency of an actual machine is less than 1 because some part of the work put into the machine is lost in overcoming the friction between the moving parts of the machine.
A lever is a simple machine which we most commonly use in our daily life. It is a rod which can turn about a fixed point called the fulcrum.
The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm
The levers are of three kinds :
Class I levers which have fulcrum in between the load and the effort.
Class II levers which have load in between fulcrum and the effort.
Class III levers which have effort in between the fulcrum and the load.
The mechanical advantage of class I lever can be 1, more than 1 or less than 1.
The mechanical advantage of class II levers is always more than 1.
The mechanical advantage of class III levers is always less than 1.
A pulley is a simple machine which is used for raising a load up by applying the effort downwards.
The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to friction, the mechanical advantage is less than 1 (i.e., the effort is more than the load).
The pulley allow us to apply the effort downwards which is a convenient direction.
The wheel and axle is a simple machine having a wheel and an axle. The linear motion of axle is obtained by rotating the wheel so as to reduce friction. Example: Steering wheel, screw drivers, water tap etc.
An inclined plane is a simple machine which is used to move a load up with a less effort. It is a sloping (or slanting) surface.
Less the slope of the inclined plane, less is the effort needed to push a load up.
The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort is required to push a heavy load up an inclined plane).
A wedge is a sharp edge formed by joining the two inclined planes together. Example: nail, knife, axe, plough etc.
A screw is a modified form of an inclined plane.
A screwjack is a simple machine having a combination of a screw and a lever. It is used to lift the heavy vehicles such as cars, trucks, buses etc.
Machines are used for our convenience. Therefore, we should take proper care of a machine by painting the machine parts to avoid rusting, lubricating its parts to reduce friction etc. This increases the life span of the machine.

Test yourself

A. Objective Questions

1. State whether the following statements are True or False.

(a) A boy does work while pushing a wall.
Answer. False

(b) A machine performs work by itself.
Answer. False

(c) In an ideal machine, work done on load is equal to the work done by effort.
Answer. True

(d) All levers are force multipliers.
Answer. False

(e) A pulley changes the direction of force.
Answer. True

(f) An inclined plane always has the mechanical advantage more than 1.
Answer. True

2. Fill in the blanks

(a) The useful work done by an actual machine is always less than the work done on the machine.
(b) In class II levers, the load is in between fulcrum and effort.
(c) The mechanical advantage of class III lever is always less than 1.
(d) A pulley is used to change the direction of effort.
(e) Mechanical advantage of an inclined plane is always greater than 1.

3. Match the following

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 1

Answer.

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 2

4. Select the correct alternatives

(a) For an ideal machine, the efficiency is

greater than unity
less than unity
equal to unity
depends on the value of load

(b) Mechanical advantage of a machine is defined as:

Load X Effort
Load / Effort
Load + Effort
Effort / Load

(c) The mechanical advantage of a lever is equal to:

Load arm / Effort arm
Effort arm / Load arm
Load arm + Effort arm
Load arn — Effort arm

(d) A pulley is used because it

has the mechanical advantage greater than one
has 100% efficiency
helps to apply the force in a convenient direction
requires more effort to raise a less load.

(e) Wheel is used with axle because

sliding friction is less than the rolling friction
rolling friction is less than the sliding friction
they work as the inclined plane
They help us to change the direction of force.

B. Short/Long Answer Questions

Question 1.
When is work said to be done by a force ?
Answer:
Work is said to be done when a force moves an obj ect through a distance in its own direction.

Question 2.
What is energy ?
Answer:
Energy: The ability or capacity to do work is called energy.

Question 3.
What do you understand by a machine ?
Answer:
Machine: A machine is a device that allows us to do work with less effort. Machines make our work easier to do. Machines have made our li ves comfortable and faster.

Question 4.
What is the principle on which a machine works ?
Answer:
Principle of a Machine: The work output of a machine is equal to the work input.

Question 5.
State two functions of a machine.
Answer:
Various functions that a machine can perform are:

Changing the direction of applied force — Example: When a flag is hoisted with the help of a pulley.
Changing the magnitude of applied force — Example: Bottle opener multiplies the applied force and much less effort is required to open the cap.
Applying force at a convenient point — Example: In a pair of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade.
Changing the speed of an object — Example: While riding a bicycle, force is applied on pedals which multiplies the speed.

Question 6.
Name six simple machines. Give an example of each machine.
Answer:
The Simple Machines and there examples are as follows:

The lever: Examples are a crow bar, claw hammer, a pair of pilers etc.
The Inclined plane: Examples are ramp, staircase, hilly roads etc.
The wedge: Examples are knife, axe, plough, nail etc.
Screw: Examples are A screw.
The wheel and axle: Examples are steering wheel of a car, bicycle pedal etc.
The pulley: Examples are a pulley used in raising a load.

Question 7.
Define the term ‘work input’ and ‘work output’ in relation to a machine.
Answer:
Work input is work done on a machine equal to the effort force times the distance through which the force is applied.
Work output is work that is done by a machine equals resistance force times the distance through which the force applied.
For an ideal machine, the work output is equal to the work input i. e. the efficiency.

Question 8.
Explain the term mechanical advantage of a machine.
Answer:
The mechanical advantage of a machine is the ratio of the load to the effort. In other words

Question 9.
Define the term efficiency of a machine.
Answer:
The ratio of the work done by the machine to the work done on the machine is called efficiency of a machine
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 5
(Work done by a machine is called the output energy and the work done on a machine is called the input energy.)

Question 10.
What is an ideal machine ?
Answer:
A machine is which no part of the work done on the machine is wasted, is called an ideal or perfect machine. Thus, for an ideal machine, the work output is equal to the work input, i.e., the efficiency of an ideal machine is 1 (or 100 per cent).

Question 11.
Can a machine have an efficiency of 100% ? Give a reason to support your answer.
Answer:
Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.

Question 12.
A machine is 75% efficient’. What do you understand by this statement ?
Answer:
If a machine is 75% efficient, it means that 75% of the work input to the machine is obtained as the useful work output. The remaining 25% of the work input has been lost in overcoming the friction.

Question 13.
What is a lever ?
Answer:
Lever: A lever is a simple rigid bar which is free to move around a point called fulcrum.

Question 14.
Describe three orders of levers giving an example of each. Draw neat diagrams showing the positions of fulcrum, load and effort in each kind of lever.
Answer:
The levers are of three kinds :
Class I levers which have fulcrum in between the load and the effort.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 6
Class II levers which have load in between the fulcrum and the effort.

Class III levers which has effort in between the fulcrum and the Load

Question 15.
What do you mean by the mechanical advantage of a lever ?
Answer:
The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm. This is also called the principle of a lever.

Question 16.
Which class of lever has the mechanical advantage always more than 1 ? Give an example.
Answer:
The mechanical advantage of class II levers is always more- than 1.
Example – Nut cracker, wheel barrow, bottle opener etc.

Question 17.
Which class of lever has the mechanical advantage always less than 1 ? Give an example.
Answer:
The mechanical advantage of class III levers is always less than 1.
Example: a pair of tongs, sugar tongs, knife, forceps etc.

Question 18.
Give one example of class I lever in each case where the mechanical advantage is

more than 1
equal to 1
less than 1.

Answer:

more than 1: Load arm of pliers
equal to 1: See – saw
less than 1: The load arm of a pair of scissors.

Question 19.
Name the class to which the following levers belong:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 9
Answer:
(a) A pair of scissors — Class I lever
(b) a lemon squeezer — Class II lever
(c) a nut cracker — Class II lever
(d) a pair of sugar tongs — Class III lever
(e) a beam balance — Class I lever
(f) an oar rowing a boat — Class I lever
(g) a wheel barrow — Class II lever
(h) a see saw — Class I lever
(i) a pair of pilers — Class I lever
(j) a crow bar — Class I lever

Question 20.
The diagram given below shows the three kinds of levers. Name the class of each lever and give one example of each class.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 10
Answer:

Examples : The examples of class I levers are : a see saw, a pair of scissors, a pair of pilers, crow bar, common balance, spoon opening the lid of a tin can, handle of a hand pump.

Examples : The examples of lever of class II are : nut cracker, wheel barrow, paper cutter, mango, lemon squeezer, bottle opener.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 13
Examples: The examples of levers of class III are : a pair of tongs, sugar tongs, knife, forceps,-forearm of a person holding a load, spade for lifting soil or coal.

Question 21.
Draw diagrams to illustrate the positions of fulcrum, load and effort, in each of the following:
(a) a see saw
(b) a beam balance
(c) a nut cracker
(d) a pair of forceps
Answer:

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 15

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 16

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 17

Question 22.
How can you increase the mechanical advantage of a lever ?
Answer:
The mechanical advantage of a lever can be increased by increasing the effort arm or reducing the load arm.

Question 23.
How does the friction at the fulcrum affect the mechanical advantage of the lever ?
Answer:
Friction at the fulcrum reduces the mechanical advantage.

Question 24.
State three differences between the three classes of levers.
Answer:

Question 25.
What is a pulley ?
Answer:
Pulley: It is a flat circular disc with a groove in its edge and a rope passing through the groove. It is capable of rotating around a fixed point passing through its central axis called axle.

Question 26.
What is the mechanical advantage of an ideal pulley ?
Answer:
In an ideal pulley, the effort applied is equal to the load to be lifted.
i.e. Effort = Load
Mechanical advantage = Load / Effort = 1

Question 27.
The mechanical advantage of an actual pulley is less than 1. Give a reason. What is the justification for using the pulley then ?
Answer:
In an actual pulley due to friction, the mechanical advantage is less than 1 (i.e. the effort is more than the load).
The reason for using the pulley when its mechanical advantage is equal to 1 or less than 1 is that the pulley allows us to apply the effort downwards i.e. in a convenient direction. To raise a load directly upwards is difficult. But with the help of a pulley, the effort can be applied in the downward direction to move the load upwards. One can hang on it to make use of his own weight also in order to apply the effort.

Question 28.
Draw a neat labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?
Answer:
To raise a load, the load is attached to one end of the string and the effort is applied at the other end by pulling it is downward direction . as shown in fig.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 19

Question 29.
What is an inclined plane? What is its use ? Give two examples where ¡t is used.
Answer:
An inclined plane is a rigid sloping surface over which heavy loads can be raised or lowered to a certain height or depth.
The mechanical advantage of an inclined plane is the ratio of the length of the plank to the vertical height of the load raised. Its value is greater than one. Therefore, an inclined plane acts as a force multiplier. Thus, it can be used to lift heavy loads.
Example : If a heavy box needs to be loaded on a lorry, it is far easier to push it over an inclined plane than to lift it up. Steeper the inclined plane, greater will be the effort required to push up the load.
Sloping ramps, flyovers, roads on hills and staircases are all examples of inclined planes.

Question 30.
What is a screw ? Give two examples.
Answer:
A screw is a simple machine which appears like an inclined plane wound around a rod with a pointed tip.
Examples : ajar lid, a drill.

Question 31.
What is wheel and axle ? Give two examples.
Answer:
The wheel and axle is a simple machine having a wheel and an axle. The linear motion of axle is obtained by rotating the wheel so as to reduce friction. Example: Steering wheel, screw drivers, water tap etc.

Question 32.
How does a wheel help in moving the axle ?
Answer:
Wheel-and-axle arrangement consists of two cylinders of different diameters joined together such that if one is made to rotate, the other also rotates. The axle is a cylindrical rod fixed to the centre of a circular disc-like object called the wheel.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 20
This machine acts as a speed multiplier device.
In riding a bicycle, when we apply force on the wheel (by pedal), the fixed axle rotates with it easily. This force that turns the axle produces a much larger movement of the wheel.

Question 33.
What is a wedge ? Give two examples.
Answer:
A wedge is a double inclined plane such that the two sloping surfaces taper to form either a sharp edge or a pointed edge. Examples : A knife, an axe, a chisel.
In some special cases, the number of inclined planes used can be more than two as well. In such cases, the sloping surfaces generally taper to form either a very sharp or a pointed edge to split or pierce materials. Pins, nails and needles are examples of pointed wedges. The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water.
The wedge works on a principle of an inclined plane.

Question 34.
Name the machine to which the following belong :

Beam balance
Lemon crusher
Sugar tongs
Ramp
Door knob
Needle

Answer:

Beam balance — A lever (lever of class I)
Lemon crusher — A lever (lever of class II)
Sugar tongs — A lever (lever of class III)
Ramp — An inclined plane
Door knob — Wheel and axle
Needle — Wedge

Question 35.
What care would you take to increase the life span of a machine which you use ?
Answer:
Taking care of machines: Some of the ways in which machines should be cared for are given below :

Machines should be kept in a clean environment, which is free from dust and moisture.
When not in use, machines should be kept covered to prevent collection of dust on them.
Machines made of iron should be protected from rust by coating them with paint.
The moving parts of a machine should be regularly oiled with a good-quality machine oil to reduce friction and wear and tear. The above care of machines increases their life.

Question 36.
Select the correct statement :
(a) A wheel barrow is a lever of class I.
(b) The efficiency of a machine is always 100%
(c) Friction in moving parts of a machine reduces its efficiency.
(d) No lever has the mechanical advantage greater than 1.
(e) It is easier to lift a load vertically up than to push it along an inclined plane.
(f) A screw is made by two inclined planes placed together.
Answer:
(c) Friction in moving parts of a machine reduces its efficiency.

C. Numericals

Question 1.
In a machine an effort of 10 kgf is applied to lift a load of 100 kgf. What is its mechanical advantage ?
Answer:
Given,
Load = loo kgf
Effort = 10 kgf
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 21

Question 2.
The mechanical advantage of a machine is 5. How much load it can exert for the effort of 2 kgf ?
Answer:
Given,
Mechanical advantage = 5
Effort 2 kgf
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 22

Question 3.
The mechanical advantage of a machine is 2. It is used to raise a load of 15 kgf. What effort is needed ?
Answer:
Given,
Mechanical advantage = 2
Load = 15 Kgf
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 23

Question 4.
A lever of length 100 cm has effort of 15 kgf at a distance of 40 cm from the fulcrum at one end. What load can be applied at its other end ?
Answer:

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 25

Question 5.
In a lever, fulcrum is at one end at a distance of 30 cm from the load and effort is at the other end at a distance of 90 cm from the load. Find :
(a) the length of load arm,
(b) the length of effort arm, and
(c) the mechanical advantage of the lever.
Answer:

Selina Concise Chemistry Class 8 ICSE Solutions – Carbon and Its Compounds

August 11, 2022December 5, 2019 by Veerendra

Selina Concise Chemistry Class 8 ICSE Solutions – Carbon and Its Compounds

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 9 Carbon and Its Compounds. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE Solutions Physics Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 9 Carbon and Its Compounds

Points to Remember:

Carbon occurs in the earth’s crust in the free as well as in the combined state.
In the free state, it occurs as coal, diamond and graphite.
In the combined state, carbon occurs in atmosphere (CO₂) natural gas, food nutrients and carbonates.
Diamond is the hardest naturally occuring substance known.
Fullerenes are discovered only recently.

Exercise – I

Question 1.
Fill in the blanks.

(a) Carbon is present in both living and non-living things.
(b) The tendency of an element to exist in two or more forms but in the same physical state is called Allotropy.
(c) Crystalline and non- crystalline are the two major crystalline allotropes of carbon.
(d) Diamond is the hardest substance that occurs naturally.
(e) The name ‘carbon’ is derived from the Latin word carbo.

Question 2.
Choose the correct alternative.

(a) In combined state, carbon occurs as
(i) coal
(ii) diamond
(iii) graphite
(iv) petroleum

(b) A crystalline form of carbon is
(i) lampblack
(ii) gas carbon
(iii) sugar
(iv) fullerene

(c) Graphite is not found in
(i) Bihar
(ii) Maharashtra
(iii) Orissa
(iv) Rajasthan

(d) Diamond is used for
(i) making the electrodes of electric furnaces.
(ii) making crucible for melting metals.
(iii) cutting and drilling rocks and glass.
(iv) making carbon brushes for electric motors.

(e) Carbon forms innumerable compounds because
(i) it has four electrons in its outermost shell.
(ii) it behaves as a metal as well as a non- metal.
(iii) carbon atoms can form long chains.
(iv) it combines with other elements to form covalent compounds.

Question 3.
Write ‘true’ or ‘false’ against the following statements.

(a) Carbon constitues 0.03% of the earth’s crust. – True
(b) Graphite is the purest form of carbon. – False
(c) Coloured diamonds are costlier than colourless and transparent diamonds. – False
(d) Graphite has layers of hexagonal carbon bondings. – True
(e) Diamond is insoluble in all solvents. – True.

Question 4.
Define the following terms:
(a) Allotropy (b) Carat
(c) Crystal (d) Catenation
Answer:
(a) Allotropy: Allotropy is defined as the phenomenon due to which an element exists in two or more forms in the same physical state with identical chemical properties but with different physical properties.

(b) Carat – The weight of diamond is expressed in carats [ 1 carat = 0.2 g]

(c) Crystal – A crystal is a homogeneous solid which particles (atoms, molecules or ions) are arranged in difinite pattern due to which they have definite geometrical shape with plane surfaces e.g. sugar and sodium chloride.

(d) Catenation – The large number of organic compounds is due to the ability of carbon atom to form long chains with other carbon atoms through the sharing of electrons. This unique property of carbon is known as catenation.
selina-concise-chemistry-class-8-icse-solutions-carbon-and-its-compounds-1

Question 5.
State the terms:

(a) Substances whose atoms or molecules are arranged in a definite pattern. – Crystals.
(b) Different forms of an element found in the same physical state. – Allotropy.
(c) The property by which atoms of an element link together to form long chain or ring compounds. – Catenation

Question 6.
Name the following:

(a) The hardest naturally occurring substance. – Diamond.
(b) A greyish black non- metal that is a good conductor of electricity. – Graphite.
(c) The third crystalline form of carbon. – Fullerenes.

Question 7.
Answer the following questions:
(a) Why is graphite a good conductor of electricity but not diamond?
(b) Why is diamond very hard?
(c) What are fullerenes? Name the most common fullerenes.
(d) What impurity is present in black diamond?
(e) Explain the softness of graphite with reference to its structure.
Answer:
(a) In a graphite molecule, one valence electron of each carbon atom remains free, Thus making graphite a good conductor of electricity. Whereas in diamond, they have no free mobile electron. Thats why diamond are bad conductor electricity.

(b) A diamond is a giant molecule. The number of valence electrons in carbon atom is four. As such each carbon atom is linked with four neighboring carbon atoms. Thus forming a rigid tetrahedral structure. It is the strong bonding’that makes diamond the hardest substance.

(c) Fullerenes: Fullerenes are the third crystalline form of carbon.
Though they were discovered only recently. They have.been found to exist in interstellar dust as well as in the geological formations of the earth.
Common fullerenes are C – 32, C – 50, C – 70 and C – 76

(d) Black diamonds have copper oxide present in them as impurity.

(e) In a graphite molecule of each carbon atoms is linked with three neighboring carbon atoms. Thus forming a hexagonal arrangement of atoms. These hexagonal grouping of carbon atoms are arranged as layers or sheets piled one the top of other. The layers are held together by weak forces such that they can slide over one another. That is why graphite is soft.

Question 8.
Give two uses of (a) graphite (b) diamond.
Answer:

(a) Uses of graphite:

For making the electrodes of electric furnaces.
For making crucibles for melting metals due to its high melting points.

(b) Uses of Diamond:

Diamond is used in jewellery as a gem
It is used for cutting and drilling rocks, glass,

Question 9.
Write three differences between graphite and diamond.
Answer:
Difference between diamond and graphite.

Diamond

Pure diamond is colourless and transparent.
It is the hardest naturally occurring substance.
It has high density i.e. 3.5 g/cm³
It is bad conduct of electricity.
It bums in air at 900°C to form carbon dioxide.

Graphite

Graphite is greyish black opaque and shiny.
It is soft and greasy to touch.
It has low density i.e. 2.39 g / cm³
It is good conductor of electricity.
It bums in air at 700° C to form carbon dioxide.

Exercise – II

Question 1.
Fill in the blanks:

(a) Charcoal is formed when charcoal is burnt in a limited supply of air.
(b) Coal is a amorphous form of carbon.
(c) Peat is the most inferior form of coal.
(d) Wood charcoal is a bad conductor of heat and electricity.
(e) lampblack is used in making black shoe polish.

Question 2.
Choose the correct alternative

(a) Anthracite is
(i) an inferior type of coal
(ii) a superior type of coal
(iii) a cheapest form of coal
(iv) none of above

(b) Destructive distillation of coal yields
(i) coal tar
(ii) coal gas
(iii) coke
(iv) all of the above

(c) Lamp black is
(i) an amorphous form of carbon
(ii) a crystalline form of carbon
(iii) a pure form of carbon
(iv) a cluster of carbon atoms

(d) The process by which decayed plants slowly convert into coal is called.
(i) petrification
(ii) carbonisation
(ii) carbonification
(iv) fermentation

(e) The purest form of the amorphous carbon is
(i) wood charcoal
(ii) sugar charcoal
(iii) bone charcoal
(iv) lampblack

Question 3.
Write ‘true’ or ‘false’ against the following statements:

(a) Charcoal is a good adsorbent. True
(b) Coke is obtained by destructive distillation of sugar. False
(c) Activated charcoal is a good conductor of electricity. False
(d) Wood charcoal is an important constituent of gun powder. True
(e) Coal gas is used in the preparation of artificial ferilizers. False.

Question 4.
Define the following:
(a) Carbonization
(b) Adsorption
(c) Bone black
Answer:
(a) Carbonization: The process of the slow conversion of vegetable matter into carbon-rich substances is called carbonization.
(b) Adsorption: Adsorption is the property due to which a substance absorbs gases, liquids and solids on its surface.
(c) Bone black: The Carbon content of bone charcoal is separated by treating the latter with hydrchloride acid, which dissolves the calcium phosphate. Carbon is then filtered out of the solution and in this form it is called bone black.

Question 5.
Name the following:

(a) Substances whose atoms or molecules are not arranged in a geometrical pattern. – Amorphous
(b) The best variety of coal. – Bituminous
(c) The purest form of amorphous carbon. – Anthracite
(d) An amorphous form of carbon that contains about 98% carbon. – Anthracite
(e) Mixture of carbon monoxide and hydrogen. – Water gas.

Question 7.
Answer the following questions:
(a) What is destructive distillation? What are the products formed due to the destructive distillation of coal?
(b) Why is wood charcoal used in water filters and gas masks?
(c) How is wood charcoal made locally? What other substances are formed in the process.
(d) How many carbon atoms are there in Buckminster fullerenes?
Answer:
(a) Destructive Distillation: When a substances is heated in the absence of air. The process is called destructive distillation.
Products formed are: Coke, Coal tar, Coal gas and ammonia solution

(b) Due to its high adsorbing capacity, wood charcoal is used as gas masks to adsorb harmful gases. Wood charcoal is porous, that is why it is used to filter water.

(c) Wood charcoal is prepared when wood is heated in a limited supply of air. Locally wood charcoal is prepared by piling logs of wood one above the other with a gap in the centre of the pile. The pile is covered with wet clay to prevent the entry of air. A few holes are left at the bottom of the pile. The wood is set on fire. After some time when fire dies out, wood charcoal is left behind. The other substances are -wood tar, pyroligneous acid and wood gas.
selina-concise-chemistry-class-8-icse-solutions-carbon-and-its-compounds-2

(d) 60 carbon atoms are arranged in spherical structure in Buck minster fullerences.

Question 7.
(a) Descirbe the formation of coal,
(b) Name four types of coal with percentage of carbon present in each, with uses.
Answer:
(a) Formation of coal:- The formation of coal took millions of years. Coal was formed by the bacterial decomposition of ancient vegetable matter hurried under successive layers of the earth. Under in action of high temperature and pressure, and in the abcence of air, the decayed vegetable matter converted into coal.
(b) Types of Coal:

Peat: It is light brown in colour and contains only 50 – 60% carbon. It is the most inferior form of coal.
Lignite: it contains more than 60% carbon. It is brown in colour and harder than peat.
Bituminous: It has 90%, 80%, 70 – 75% carbon contents. Bituminous coal is the most common variety of coal and used as house hold coal.
Anthracite: It is the purest variety of coal. Its carbon contents vary between 92 – 98%. It is hard, dense and black, difficultto ignite.

Uses of coal:

Coal is used as both domestic and industrial fuel.
It is used to prepare coke, coal gas and coal tar.

Question 9.
Name the products formed when:
(a) wood is burnt in the absence of air.
(b) bone is heated in the absence of air.
(c) diamond is burnt in air at 900°C.
(d) graphite is subjected to high pressure and 3000°C temperature.
Answer:
(a) Wood charcoal is formed when wood is burnt in limited supply of air.
(b) Bone charcaol, bone oil and organic compound pyridine.
(c) Carbon dioxide.
(d) Artificial diamond.

Question 9.
Give two uses for each of the following:
(a) coal
(b) coke
(c) wood charcoal
(d) sugar charcoal
(e) bone charcoal
(f) lampblack
Answer:
(a) Uses of coal

It is used as both a domestic and an industrial fuel.
It is used to prepare coke, coal gas and coal tar.

(b) Uses of coke

Coke is used as a smokeless fuel, in smelting furnaces.
It is used in the manufacturing of water and producer gas.

(c) Uses of wood charcoal:

Wood charcoal is used as a fuel.
It is an important constituent of gun powder.

(d) Sugar charcoal:

Sugar charcoal is mostly used as a reducing agent.
It is used to decolourise coloured solutions.

(e) Bone charcoal:

It is extensively used to decolourise cane-sugar in the process of manufacturing sugar.
It is also used in the manufacture of large number of phosphorous compounds.

(f) Uses of lamp black:

It is used in making black shoe polish.
It is used in the manufacture of tyres and gun powder.

Question 10.
Give balanced equations for the following chemical reactions:
(a) wood charcoal and cone, nitric acid
(b) coke and steam
(c) wood charcoal and lead monoxide.
Answer:

Exercise – III

Question 1.
(a) Name the chemicals required for the preparation of carbon dioxide in the laboratory.
(b) How will you collect the gas ?
(c) Write the balanced chemical equation for the above reaction.
(d) Draw a labelled diagram for the preparation of CO₂ in the laboratory.
(e) Why is sulphuric acid not used for the preparation of carbon dioxide in the laboratory ?
Answer:
(a) Calcium carbonate and dilute hydrochloric acid.
(b) By upward displacement of air.
(c) CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
(d) Laboratory preparation of carbon dioxide

(e) Dilute sulphuric acid reacts with calcium carbonate. But it is not used because the calcium sulphate which is formed during the reaction is insoluble in water. It covers the marble chips and stops the reaction.

Question 2.
Write the balanced chemical equations for the preparation of carbon dioxide by:
(a) heating calcium carbonate.
(b) the action of acetic acid on sodium bicarbonate.
(c) the action of dilute sulphuric acid on sodium bicarbonate.
Answer:

Question 3.
What happens when:
(a) a lit splinter is introduced into a jar containing carbon dioxide ?
(b) moist blue litmus paper is placed in a jar containing carbon dioxide ?
(c) carbon dioxide is passed through lime water first in small amounts and then in excess ?
(d) a baking mixture containing baking powder is heated?
(e) a soda water bottle is opened ?
Answer:
(a) Lit splinter extinguishes.
(b) Blue litmus paper turns red.
(c) When CO₂ is passed through lime water in small amount, it turns milky, when passed in excess milkiness disappears.
(d) Carbon dioxide is formed.
(e) When the pressure is released the bottled gas escapes with a bristling effervescence that ads fizz to the drink.

Question 4.
Give reasons for the following:
(a) An excess of carbon dioxide increases the temperature of the earth.
(b) Soda acid and foam types of fire extinguisher are not used for extinguishing electrical fires.
(c) Solid carbon dioxide is used for refrigeration of food.
Answer:
(a) Excess of carbon dioxide increases the temperature of the earth. Due to rise in temperature ice in the polar regions may melt causing floods in coastal regions island.
(b) In both of these fire extinguishers, the solutions are prepared in water, which conducts electricity. As a result an electric shock might result, which might lead to short- circuiting and another fire.
(c) Solid carbon dioxide serves as a coolant and refrigeration for preserving food articles.

Question 5.
What is a fire extinguisher ? What is the substance used in the modern type of fire extinguishers ? How is it an improvement over the soda acid-type and the foam-type fire extinguishers ?
Answer:
Fire Extinguisher— Fire extinguishers are a device in which carbon dioxide is produced in different forms for use as the extinguishing agent. It is a modem type of fire extinguisher in which liquid carbon dioxide is stored in a steel cylinder under pressure. Soda-acid and foam types of extinguisher cannot be used for extinguishing fire as they prepared in water, which conducts electricity and there can be short circuiting, causing another fire.

Question 6.
Explain the term ‘green house effect’. How can it be both beneficial and harmful for life on earth ?
Answer:
Green house effect— The trapping of the earth’s radiated energy by carbon dioxide present in air, so as to keep the earth warm, is called ‘green house effect’.
Green house is beneficial because this principle is applied to grow plants in colder regions.
Carbon dioxide increases the temperature of atmosphere. Due to rise in temperature; ice in the polar regions may melt, causing floods. So it is harmful for life on earth.

Question 7.
What steps should be taken to balance carbon dioxide in the atmosphere ?
Answer:
As global warming will cause an unbalanced ecological system, serious efforts should be made to balance the percentage of carbon dioxide in the atmosphere. Some of these steps are:

Growing more trees and plants.
Using smokeless sources of energy like solar energy, biogas, etc.
Using filters in the chimneys of factories and power houses.

Question 8.
State three ways by which carbon dioxide gas is added into the atmosphere.
Answer:

By planting more trees.
By combustion of fuels
By decay of dead animals, plants and plants products.

Exercise – IV

Question 1.
Fill in the blanks:

(a) Carbon monoxide is formed when carbon is burnt in a limited supply of air or oxygen.
(b) Carbon monoxide bums in air with a pale blue flame to form carbon dioxide.
(c) Carbon monoxide is a products of incomplete combustion.
(d) A mixture of 95% oxygen and 5% carbon dioxide is called carbogen
(e) Carbon dioxide is used as a reducing agent in the extraction of pure metals from their corresponding ores.

Question 2.
Match the following.
selina-concise-chemistry-class-8-icse-solutions-carbon-and-its-compounds-7

Question 3.
How is carbon monoxide gas formed?
Answer:
Mostly carbon monoxide is formed when a large amount of carbon or its compounds is burnt in a limited supply of air or oxygen.
selina-concise-chemistry-class-8-icse-solutions-carbon-and-its-compounds-8

Question 4.
State the poisonous nature of carbon monoxide?
Answer:
Carbon monoxide is highly poisonous gas. If air containing 0.5% carbon monoxide by volume is inhaled, death can result This is because carbon monoxide combines with the haemogloblin present in the blood cells of our body to form a stable compound called carboxyl-haemoglobin. This does not allow to absorb oxygen. Thus depriving our body cells of oxygen. This cause obsruction in respiration and causes death.

Question 5.
Give two uses of carbon monoxide.
Answer:
Uses of carbon monoxide:

Carbon monoxide is a strong reducing agent.
Carbon monoxide is used in the extraction of pure metals from their ores.

Question 6.
Why is carbon monoxide called silent killer ?
Answer:
Carbon monoxide is produced by burning coal or wood in a limited supply of air. Since the gas is colourless and a barely detectable smell, people do not feel it and it can be proved as a silent killer.

Question 7.
Explain the reducing action of carbon monoxide.
Answer:
Reducing action of carbon- monoxide: Carbon monoxide is a strong reducing agent. It reduces the oxides of the less active metals to their respective metals and itself gets oxidised to carbon dioxide.
selina-concise-chemistry-class-8-icse-solutions-carbon-and-its-compounds-9

Question 8.
Write two remedies for carbon monoxide poisoning.
Answer:

The victim should immediately brought out into the open.
The victim should be given artificial respiration with caibogen.

Question 9.
Complete the reactions and balance them.
(a) CuO + CO →
(b) Fe₂O₂ + CO →
Answer:

Selina Concise Physics Class 6 ICSE Solutions – Matter

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Physics Class 6 ICSE Solutions – Matter

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

Selina Class 6 Physics ICSE Solutions Chemistry Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 6 Physics Chapter 1 Matter

Synposis

Matter is the substance which occupies space and has mass.
The three states of matter are

solid,
liquid
gas.

Matter is composed of large number of molecules.
A molecule is the smallest particle which can exist freely in nature by itself and it retains the properties of the substance.
All molecules of a substance are identical, but the molecules of different substanes are different.
A molecule is very small in size (10^-10 m).
The molecules are separated from each other with spaces called inter-molecular spacing.
The molecules in a substance are held together by the forces acting between the molecules which are called the inter-molecular forces.
The force of attraction between the molecules of the same sub¬stance is called the force of cohesion, while the force of attraction between the molecules of two different substances is called the force of adhesion.
The forces of cohesion and adhesion are effective only when the separation between the molecules is 10^-9 m. When the separation becomes more, they vanish.
The molecules in a substance are not at rest, but they are con¬stantly in motion.
In a solid, the molecules are rigid, the inter-molecular spacing is least, the inter-molecular forces are strongest and the molecules remain in their fixed positions. They vibrate to and fro about their mean positions, but they do not leave their positions, so a solid has a definite shape and a definite volume.
In a liquid, the molecules are not rigid, the inter-molecular spacing is more than that in solids, the inter-molecular forces are weak and the molecules are free to move within the boundary of the liquid, so the liquid has a definite volume, but it does not have a definite shape.
In gases, the molecules are not rigid, the inter-molecular spacing is more than that in solids and liquids, the inter-molecular forces are weakest and the molecules are free to move anywhere in space. So the gas has neither a definite volume nor a definite shape.

Activity – 2

Classify 20 objects around you as solids, liquids and gases

Solids : Ice, Aluminium, Silver, Calcium, Gold, Iron, Sodium, chloride, Sugar, Wood.

Liquids : Water, benzene, chloroform, oil, honey, glycerine, hydrochloric acid, alcohol, dettol.

Gases : Steam, Air, Oxygen, Hydrogen, Chlorine, Nitrogen, Ammonia, Helium, Argon.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) The molecules of each substance are identical.
Answer. False

(b) The inter-molecular forces are effective at all distances between the two molecules.
Answer. False

(c) The molecules in a substance arc in random motion.
Answer. Tme

(d) In a gas, the molecules can move anywhere in space. .
Answer. Tme

(e) The liquids are less viscous than the gases.
Answer. False

2. Fill in the blanks

(a) All the molecules of a substance are identical.
(b) The inter-molecular spacing is least in solids more in liquids and still more in gases.
(c) The molecular motion in liquid and gas is in zig-zag path.
(d) In a solid, the molecules vibrate to and fro but they remain at their fixed positions.
(e) The inter-molecular forces are the weakest in gases.
(f) A solid exerts pressure downwards on its base.
(g) The gases are least dense.
(h) A solid is most rigid.

3. Select the correct alternative

(a) The diameter of a molecule is approximately

1 cm
10 cm
10^-10 m
1 m

(b) The inter-molecular forces are strongest in

solids
liquids
gases
both (i) and (ii)

(c) The molecules

in solid, liquid and gas, move freely anywhere.
in a solid, move freely within its boundary.
in a liquid, move within its boundary.
in a gas, move only within its boundary.

(d) The solids are

more dense
less dense
least dense
highly compressible

(e) The inter-molecular forces in liquids are

as strong as in solids
stronger than in solids
weaker than in solids
weaker than in gases

4. Match the following columns

Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 2

B. Short/Long answer questions

Question 1.
Define matter. What is its composition ?
Answer:
Matter is defined as anything which occupies space and has mass. It can be perceived by our sense of smell, touch, sight, hearing and taste.
Matter is composed of tiny particles known as atoms.

Question 2.
Name the three states of matter.
Answer:
The three states of matter are solids, liquids and gases.
Solids —A solid has a definite shape and definite volume.
Example – wood, stone, iron, ice etc.
Liquid —A liquid has a definite volume but not definite shape.
Example — water, juice, milk, oil, etc.
Gases —A gas neither has definite shape nor a definite volume.
Example – air, hydrogen, oxygen, water vapour etc.

Question 3.
What is a molecule ?
Answer:
The smallest unit of matter which can exist independently is called molecule.
Example: Oxygen molecule (O₂) made up of two (O) atoms.

Question 4.
What is the approximate size of a molecule ?
Answer:
Matter is made up of molecules which are very small in size (~10^-9m).

Question 5.
One litre of water has 6.02 × 10²⁶ molecules. Estimate the size of a molecule.
Answer:
The size of a particle (or molecule of matter is very small. 1 litre of water has 6.02 × 10²⁶ molecules, so the volume of a particle of
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 3
Thus the diameter of a water molecule is nearly 1.27 × 10^-9 metre.

Question 6.
What do you mean by inter-molecular spacing ?
Answer:
Intermolecular space — The space between any two consecutive molecules of a substance is called intermolecular space

Question 7.
Describe a simple experiment to illustrate the existence of inter-molecular spacing.
Answer:
Take 100 ml of water in a measuring cylinder. Add 20 gram of salt in water gently and stir it well so as to dissolve the salt well in water. It is noticed that the level of water does not change. It shows that the particles of salt occupy spaces between the particles of water.
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 4

Question 8.
What do you mean by inter-molecular forces ?
Answer:
Intermolecular force of attraction — The force of attraction between the molecules (like molecules or unlike molecules) is called intermolecular force of attraction.

Question 9.
What are the forces of cohesion and adhesion ?
Answer:
The force of attraction between the molecules of similar kind is called force of cohesion.
Example: The forces between water molecules.
This force of cohesion keep the molecules of the substance bind together.
The force of attraction between different types of molecules is called force of adhesion.
Example: When a glass filled with water is emptied some water I particles remain stuck to the glass due to the adhesion between water molecules and glass.

Question 10.
State three characteristics of molecules of matter.
Answer:
The particles of matter called molecules, have the following characteristics:

They are very small in size.
They have spaces between them.
They are in constant random motion.
They always attract each other.

Question 11.
State the approximate spacing between two molecules of a matter.
Answer:
The spacing between particles of a matter is called inter-molecular space.

Question 12.
How do the solids, liquids and gases differ in their following properties
(a) Size
(b) Shape
(c) Density
Answer:

Question 13.
The molecules in a substance are in motion. What type of path do they follow ?
Answer:
The particles in a substance are not at rest (in motion),and they move randomly in all possible directions in a zig-zag Path

Question 14.
Describe a simple experiment to illustrate that molecules are not at rest, but they constantly move.
Answer:
Take a beaker. Fill it partly with water. Add some lycopodium powder in the beaker containing water. Stir the contents of the beaker with a glass rod. Take out few drops of this suspension on a glass plate. Place it on the table and illuminate it with a table lamp. Observe the glass plate through a microscope. It is found that the fine particles of lycopodium powder move rapidly in a random manner and their path is zig zag as shown in figure below.
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 6

Question 15.
Write down five general properties of solids, liquids and gases.
Answer:
Solids:

The molecules here are very tightly packed having negligible or very less intermolecular space.
They have the strongest intermolecular force of attraction.
The molecules have very small vibration about their mean position i.e. small amplitude.
They have a definite shape and volume.
They are generally hard and rigid.
They are good conductors of heat.

Liquids:

Molecules are less tightly packed.
The intermolecular force of attraction is less than that of solids.
The molecules here can move from one place to another
Do not have any particular shape of their own and thus acquire the shape of the vessel.
A particular quantity of a liquid has a definite volume at a given temperature.

Gases :

The force of attraction between the molecules is the least.
The intermolecular space is the largest.
Neither have a definite shape nor a definite volume.
The molecules move independently.
Worst conductors of heat.

Question 16.
Give the molecular model for a solid and use it to explain why a solid has a definite volume and a definite shape.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 7
Here the molecules are very tighty packed that there is no or very less intermolecular space and there is high intermolecular force of attraction (force of cohesion).
The molecules do not move about their mean position and thus solids have a definite shape and volume.

Question 17.
Describe the molecular modcl for a liquid. I-low does it explain that a liquid has no definite shape, but has a definite Volume ?
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 8
Here the molecules are less tightly packed as compared to solids and also there is lesser force of intermolecular attraction. The intermolecular distance is greater than that in the solids. Thus, they do not have a definite shape but acquire the shape of the vessel in which they are contained but have a definite volume at a given temperature.

Question 18.
A gas has neither a definite volume nor a definite shape. Describe the molecular model to explain it.
Answer:
Here the molecules are far apart from each other i.e. have the greatest intermolecular distance which result into the weakest intermolecular forces of attraction. The molecules as are not
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 9
bound by any strong force move about freely and thus gases do not have a definite shape and also do not have any definite volume.

Question 19.
Distinguish between the three states of matter—solid, liquid and gas on the basis of their molecular models.
Answer:
Solids:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 10
Here the molecules are very tighty packed that there is no or very less inteimolecular space and there is high intermolecular force of attraction (force of cohesion).
The molecules do not move about their mean position and thus solids have a definite shape and volume.
Liquids:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 11
Here the molecules are less tightly packed as compared to solids and also there is lesser force of intermolecular attraction. The intermolecular distance is greater than that in the solids. Thus, they donot have a definite shape but acquire the shape of the vessel in which they are contained but have a definite volume at a given temperature.
Gases :
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 12
Here the molecules are far apart from each other i.e. have the greatest intermolecular distance which result into the weakest intermolecular forces of attraction. The molecules as are not bound by any strong force move about freely and thus gases do not have a definite shape and also do not have any definite volume.

Question 20.
Distinguish between solids, liquids and gases on the basis of their following properties :
(a) compressibility
(b) fluidity
(c) rigidity
(d) expansion on heating
Answer:

Question 21.
What do you mean by the change of state of matter ? Explain:
(a) the change of a solid into a liquid at a constant temperature, and
(b) the change of a liquid into a gas at a constant temperature.
Answer:
The change in state of matter of a substance from solid to liquid or from liquid to gas is brought by imparting heat energy to it at a constant temperature.
(a) The process of change of a substance from solid state into its liquid state on absorption of heat at a particular temperature, called the melting point, is called melting or fusion i. e.

(b) The process of change of a substance from a liquid state to its gaseous state at a particular temperature, called the boiling point,
is called boiling or vaporisation, i.e.

Selina Concise Physics Class 6 ICSE Solutions – Physical Quantities and Measurement

August 11, 2022December 5, 2019 by Kalyan

Selina Concise Physics Class 6 ICSE Solutions – Physical Quantities and Measurement

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

Selina Class 6 Physics ICSE Solutions Chemistry Biology Maths Geography History & Civics

Selina Concise ICSE Solutions for Class 6 Physics Chapter 2 Physical Quantities and Measurement

Synposis
The observation of a phenomenon is made possible by using the five senses: sight, smell, touch, hearing and taste.
Our senses are not always reliable. They are subjective.
Sometimes it is necessary to make an exact measurement.
Physics is a science of measurement.
We use instruments to get an exact measurement.
Four basic measurements in our daily life are: measurement of length, measurement of mass, measurement of time, and measurement of temperature.
Measurement is basically a process of comparison of the given quantity with a standard unit.
For measuring a quantity we need a unit, and then we find the number of times that unit is contained in that quantity.
The unit selected for measurement should be of a convenient size and it must not change ‘with place or time.
The distance between two fixed points is called length.
The S.I. unit of length is metre (m). Its multiple is kilometre (km), where 1 km = 1000 m. Its sub multiples are centimetre (cm) and millimetre (mm), where 1 cm = 10^-2 m and 1 mm = 10^-3 m.
The FPS unit of length is foot (ft) and its sub multiple is inch where 1 ft = 12 inch and 1 ft = 30.48 cm.
The most common instruments used to measure length are the metre ruler and the measuring tape which are marked in cm and mm.
To measure a length accurately with a metre ruler, the scale should be placed with its markings close to the object and parallel to its r length. The eye is kept in front of and in line with the reading to be taken.
The quantity of matter contained in a body is called its mass.
The S.I. unit of mass is kilogram (kg). Its multiples are quintal and metric tonne. 1 quintal = 100 kg and 1 metric tonne =10 quintal = 1000 kg. Its sub multiples are gram (g) and milligram (mg) where 1 g = 10 kg and lmg = 10^-6 kg.
The FPS unit of mass is pound (lb) where 1 lb = 453.59 g.
Mass of a body is measured by using a beam balance or an electronic balance.
The interval between two instances or events is called time.
The S.l. unit of time is second (s), 1 s 1 / 86400 of a mean solar day. The C.G.S. and F.P.S. unit of time is also second (s).
The multiple unit of time are minute (mm), hour (h), day and year where 1 min = 60 s, 1 h = 3600 s, 1 day = 86400 s and 1 year = 3.15 × 10⁷ s.
The time at any instant is recorded by a pendulum clock or watch and the time interval of an event is measured by using a stop watch or a stop clock.
The temperature is the measure of degree of hotness or coldness of a body.
The S.I. unit of temperature is kelvin(K), but the common unit of temperature is degree Celsius (°C) and degree fahrenheit (°F).
Doctors use a clinical thermometer to measure the patient’s body temperature.
The normal temperature of a human body is 37°C or 98.6°E
The total surface occupied by an object is called its area. Area is expressed as the product of measured length of two sides.
The S.I. unit of area is square metre (m²).
One square metre is the area of a square of each side one metre.
The bigger (or multiple) units of area are dam², hectare and square kilometre (km²), where 1 dam² =100 m²,1 hectare= 10⁴ m² and 1 km² = 10⁶^m2
The smaller (or sub multiple) units of area are cm² and mm² where 1cm² = 10^-4 m² and 1 mm² = 10^-6m²

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) S.I. unit of temperature is Fahrenheit.
Answer. False

(b) Every measurement involves two things – a number and a unit
Answer. True

(c) Mass is the measure of quantity of matter.
Answer. True

(d) The S.I. unit of time is hour.
Answer. False

(e) The area can be expressed as the product of length of two sides.
Answer. Tme

2. Fill in the blanks

(a) The S.I. unit of length is metre of time is second of mass is kilogram.
(b) °C is the unit of temperature.
(c) 1 metric tonne = 1000 kg
(d) The zero mark in Celsius thermometer is the melting point of ice
(e) The thermometer used to measure the human body temperature is called the clinical thermometer.
(f) The normal temperature of human body is 37 °C or 98.6 °F.
(g) The mass of an object is measured with the help of a beam balance.

3. Match the following columns

4. Select the correct alternative

(a) The symbol of degree celsius is

(b) lO mm is equal to

1cm
1m
10dm
10cm

(c) The amount of surface occupied by an object is called its:

volume
area
mass
length

(d) A metre ruler is graduated in:

(e) A thermometre is graduated in:

kelvin
°C
g
cm

B. Short/Long Answer Questions

Question 1.
What is measurement ? How is a measurement expressed ?
Answer:
Measurement is a comparison of an unknown quantity with a known fixed quantity of the same kind.
The value obtained on measuring a quantity is called its magnitude. The magnitude of a quantity is expressed as numbers in its unit.

Question 2.
State two characteristics of a unit.
Answer:
Two characteristics of a unit are

It should be of convenient size.
It must be universally accepted, i. e. its value must remain same at all places and at all times.

Question 3.
Name four basic measurements in our daily life.
Answer:
In our daily life we measure the following four basic physical quantities.

Length
Mass
lime
Temperature

Question 4.
What are the S.I. units of

mass
length
time and
temperature. Write their names and symbols.

Answer:
S.I. units are as follows
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 2

Question 5.
Define one metre, the S.I. unit of length. State its one multiple and one sub multiple.
Answer:
One metre is defined as the distance travelled by light in air in \(\frac { 1 }{ 299,792,458 }\) of a second
Multiple of metre = Kilometre
Submultiple of metre = Centimetre

Question 6.
Convert the following quantities as indicated
(a) 12 inch = ft
(b) 1 ft = cm
(c) 20 cm = m
(d) 4.2 m = cm
(e) 0.2 km = m
(f) 0.2 cm = mm
(g) 1 yard = m
Answer:
(a) 12 inch 1 ft
(b) 1 ft = 30.48cm
(c) 100 cm = 1m
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 3

Question 7.
(a) Describe in steps how would you measure the length of a pencil using a metre rule. Draw a diagram if necessary.
Answer:
To measure the length of a pencil using a metre rule, place metre rule with its marking close to the object. Let PQ be a pencil.
The end P of the pencil coincides with the zero mark on the ruler. The end Q of the pencil is read by keeping the eye at the position ‘B’ vertically above the end Q. So the length of pencil is 4.3 cm.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 4
(b) Explain with an example how you will use the metre ruler in part (a) if the ends of ruler are broken.
Ans. The ends of the ruler get damaged with use and its zero mark may not be visible. To measure the length of an object with such a ruler, the object is placed close to a specific markings on the ruler and positions of both ends of the object are read on the ruler.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 5
The difference of the two readings gives the length of the object. In fig. the reading on ruler at the end X is 1.0 cm and at the end Y is 4.3 cm. So the length of the rod XY is 4.3 — 1.0 = 3.3 cm.

Question 8.
Name the device which you will use to measure the perimeter of your play ground. Describe in steps how you will use it.
Answer:
We will use a measuring tape to measure the perimeter of our playground.
To measure the length of playground the tape is spread along the length of the curved area.

Question 9.
The diagram below shows a stick placed along a metre RULER. The length of the stick is measured keeping the eye at positions A, B and C.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 6
Answer:
(a) Write the length if stick PQ as observed, for each position of the eye. Are they all same?
Ans. Length of stick PQ from
Position A =3.4 cm
Position B = 3.2 cm
Position C = 3.00 cm
No they are not same.
(b) Which is the correct position of the eye? Write the correct length of the stick.
Ans. ‘B’ is the correct position of the eye. Correct length of the stick PQ = 3.2 cm

Question 10.
Define mass. State its (1) S.I. (2) C.GS and (3) EP.S. units. How are they related ?
Answer:
The mass of a body is the quantity of matter contained in it. The S.I. unit of mass is kilogram. In short form, it is written as kg.
In C.GS. system, the unit of mass is gram, (symbol g).
In F.P.S. system, the unit of mass is pound (symbol lb)

Question 11.
Convert the following quantities as indicated:
(a) 2500 kg = ………. metric tonne.
(b) 150 kg = quintal
(e) 10 lb = ………. kg
(d) 250 g = … .kg
(e) 0.01 kg = ………. g
(f) 5 mg = ………. kg
Answer:

Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 8

Question 12.
Name the instrument which is commonly used to measure the mass of a body. State how is it used ?
Answer:
Instrument commonly used to measure the mass of a body, is the beam balance.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 9
When we hold up the balance, we observe that when there is nothing on either pan, the beam is horizontal. The body whose mass is to be measured is placed on the left pan. The standard weight are put on the right pan. They are so adjusted that the beam is again horizontal on holding the balance up. The total of the standard weights gives the mass of the given body.

Question 13.
Define one kilogram, the S.I. unit of mass. How is it related to (i) quintal (ii) metric tonne and (iii) gram.
Answer:
The mass of 1 litre of water at 4 °C is taken as 1 kilogram
1 quintal = 100 kg
1 metric ton = 10 quintal = 1000 kg

Question 14.
Name and define the S.I. unit of time. How is it related to (i) minute (ii) hour, (iii) day and (iv) year ?
Answer:
The S.I. unit of time is second. In short form we write it as ‘ S ’.
One second is the time interval between the two consecutive ticks that you hear from pendulum wall clock.
1 min = 60 s
1 h = 60 min. = 3600 s.
1 day = 24 h = 86400 s.
1 year = 365 days = 3.15 × 10⁷ s.

Question 15.
Name two devices used to measure the short time interval of an event.
Answer:
Two devices used to measure the time interval of an event are

StopWatch
Stop Clock

Question 16.
Express in second

3 minute 15 second and
5 hour 2 minute 5 second.

Answer:

3 minute = 15 second
1 minute = 60 second
3 minutes 15 second = 60 × 3 + 15
= 180 + 15
= 195 seconds
1 minute =60 second
2 minutes =2 × 600 = 120 second …(1)
1 hour 3600 second
5 hour 3600 × 5 = 18000 second …(2)
5 hour 2 minutes and 5 second
= 18000 + 120 + 5 = 18125 seconds

Question 17.
What does the temperature measure ?
Answer:
Temperature measures the degree of coldness and hotness of a body.

Question 18.
Name the

S.I. unit and
one common unit of temperature. Write their symbols also.

Answer:
The S.I. unit of temperature is kelvin (symbol K).
Common unit of temperature is degree centigrade (symbol °C)

Question 19.
Name the instrument used for measuring of the temperature of a person. Draw its labelled neat diagram.
Answer:
The temperature is measured with a thermometer.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 10

Question 20.
Write the temperature of (i) melting ice (ii) boiling water.
Answer:
The temperature of

melting ice = 0 °C
boiling water = 100 °C

Question 21.
What is a clinical thermometer ? State its special feature. Draw a labelled neat diagram of a clinical thermometer showing the range of temperature marked on it.
Answer:
Doctors use a special thermometer called the clinical thermometer for measuring the temperature of the patient’s body. This thermometer has the markings from 35°C to 42°C. It has a slight bend or kink in the stem just above the bulb. This kink is called the constriction. This constriction prevents the mercury from falling back all by itself. The temperature of a healthy person is 37°C. This temperature is marked by a red arrow.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 11

Question 22.
What is the normal temperature of the human body ? How is it indicated in a clinical thermometer ?
Answer:
Normal temperature of a human body is 37°C or 98.6 °F.
To measure the temperature of a patient’s body, its bulb is kept either below the tongue or under the arm’s pit of the patient for about a minute. Then the thermometer is taken out and its reading is noted. When the temperature of patient’s body is above 37°C, he is said to suffer with fever.

Question 23.
Can a clinical thermometer be used to measure the temperature of the boiling water ? Give reason for your answer.
Answer:
No, a clinical thermometer cannot be used to measure the temperature of boiling water. ,
The reasons are

It has a very small range.
It can break on cooling and on excess heating.

Question 24.
Explain the term ‘area of a surface’.
Answer:
The total surface occupied by an object is called its area or surface area.

Question 25.
Name the S.I. unit of area and define it.
Answer:
The S.I. unit of area is square metre or meter² which in short form is written as m².

Question 26.
How are the units

square yard
hectare
km²
cm²
mm² related to the S.I. unit of area ?

Answer:

Question 27.
Explain how you will measure the area of (i) a square (b) a leaf?
Answer:
The area of a square can be calculated by using the following formula –
1. Area of square of side l
= side x side
= l × l = L² .
The area of a leaf is obtained by using a graph paper. A graph paper has small squares of each side 1 mm. The area of each big square is 1 cm².
Procedure: Place the leaf on graph paper. Draw its outline on the paper and remove it. Now count the number of complete squares. To this add the number of incomplete squares which are half or more than half. Ignore the squares which are less than half. Thus,
Approximate area = (No. of complete squares + no. of half or more than half of incomplete squares) × area of one square.

Selina Concise Chemistry Class 8 ICSE Solutions – Matter

August 11, 2022December 5, 2019 by Veerendra

Selina Concise Chemistry Class 8 ICSE Solutions – Matter

ICSE Solutions Selina ICSE Solutions ML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter

Exercise

Question 1.
Define:
(a) matter
(b) intermolecular force of attraction.
Answer:
(a) Matter is anything which has mass, occupies space and can be percieved by our senses.
Example: Air, Book.
(b) The molecules of matter are always in motion and attract each other with a force called intermolecular force of attraction due to which they are held together.

Question 2.
What are the three states of matter ? Define each of them with two examples.
Answer:
The three states of matter are:
solids, liquids and gases

Solids — A solid has a definite shape and definite volume.
Example – wood, stone, iron, ice etc.
Liquid — A liquid has a definite volume but not definite shape.
Example — water, juice, milk, oil, etc.
Gases — A gas neither has definite shape nor a definite volume.
Example – air, hydrogen, oxygen, watervapour etc.

Question 3.
Define interconversion of states of matter. What are the two factors responsible for the change of states of matter?
Answer:
The process by which matter changes from one state to another and back to original state, without any change in its chemical composition is called interconversion state of matter.
Two factors responsible for change of state of matter are: change in
(i) Temperature (ii) Pressure

Question 4.
State the main postulates of kinetic theory of matter.
Answer:
The main postulates of the theory are:

Matter is composed of very small particles called atoms and molecules.
The constituent particles of a kind of matter are identical in all respects.
These particles have space or gaps between them which is known as interparticular or intermolecular space.
There exists a force of attraction between the particles of matter which holds them together. This force of attraction is known as interparticular or intermolecular force of attraction.
Particles of matter are always in a state of random motion and possess kinetic energy, which increases with increase in temperature and vice-versa.

Question 5.
What happens to water if
(a) it is kept in a deep freezer
(b) it is heated
Explain the phenomenon of change of state of water.
Answer:
(a) When water is kept in a deep freezer, it gets cooled and change into ice at 0°C ice.

(b) Water on heating changes into steam at 100°C

Phenomenon of change of state of water:
Water is a liquid under ordinary conditions but, when it is kept in a deep freezer, it changes into ice at 0°C and when ice is kept at room temperature again changes back into liquid water.
Similarly, water on heating change into steam at 100°C, which on cooling changes back into liquid water. But there is no change in the chemical composition of water. When its state changes from liquid to solid or liquid to gaseous state.

Question 6.
(a) State the law of conversation of mass.
(b) What do you observe when, barium chloride solution is mixed with sodium sulphate solution ?
Answer:
(a) “Matter can neither be created nor be destroyed in a chemical reaction”. However, it may change from one form to another in the process.
It can also be stated as, “In a chemical reaction, the total mass of the reactants is equal to the total mass of the products”.

(b)

We will observe that a white insoluble solid (precipitate) of barium sulphate is formed along with a solution of sodium chloride. Wait for ten minutes to complete the reaction and the solid formed to settle down.
Weigh the content again and note the reading.
We will observe that,
total mass of the apparatus + reactants = total mass of apparatus + products
Hence the law of conservation of mass is verified.

Question 7.
Give reasons:
(a) A gas can fill the whole vessel in which it is enclosed.
(b) Solids cannot be compressed.
(c) Liquids can flow.
(d) When magnesium is burnt in air, there is an increase in mass after the reaction.
Answer:
(a) Because, in gases, the molecules are free to move.
They are not stuck to each other and the intermolecular force of attraction is least in the gases. So the gas almost filled the whole vessel in which it is enclosed.

(b) In solids, particles are closely packed. There is a strong force of attraction and the intermolecular space is almost zero. Therefore the molecules are not free to move, which makes them hard and rigid. So solids can not be compressed.

(c) In liquids intermolecular force is weaker because the particles are not closely packed and hence there is large intermolecular space. So molecules in a liquids can move randomely and hence liquids can flow easily.

(d) When magnesium ribbon is burnt in air, a white solid, magnesium oxide is formed. The mass of magnesium oxide is
more than the mass of magnesium. This is because mass of oxygen used is not taken. If that is considered, the total mass of the reactants and the products is found to be almost equal.

Question 8.
Fill in the blanks:

(a) The change of a solid into a liquid is called melting or fusion.
(b) The process in which a solid directly changes into a gas is called sublimation.
(c) The change of water vapour into water is called condensation.
(d) The temperature at which a liquid starts changing into its vapour state is evaporation or vaporisation.

Question 9.
Give two examples for each of the following:
(a) The substances which sublime.
(b) The substances which do not change their state on heating.
Answer:
(a) Camphor, iodine, naphthalene, ammonium chloride, dry ice (solid carbon dioxide), etc.
(b) Gases do not change their state on heating.
Example: O₂.

Question 10.
Define:
(a) Diffusion.
(b) Brownian motion.
Answer:
(a) Diffusion: The intermixing of two or more substances due to the motion of their particles in order to get a uniform mixture is called ‘diffusion’.
(b) Brownian motion: The haphazard, random motion of suspended particles on the surface of a liquid or in air is called ‘Brownian motion’.

Question 11.
When sodium chloride is added to a definite volume of water and stirred well, a solution is formed, but there is no increase in the level of water. Why?
Answer:
This is because there is some space between the particles of water in which the salt particles get accomodated when dissolved.

Question 12.
What do you observe when a gas jar which appears empty is inverted over a gas jar containing Bromine vapours? Name the phenomenon.
Answer:
When a gas jar full of bromine vapours (reddish brown) is inverted over a gas jar containing air over it. It is observed that after sometime, the reddish brown vapours of bromine also spread out into the upper jar. This mixing is called diffusion. The rate of diffusion is the fastest in gases and the slowest in solids. It increases with an increase in temperature.

Question 13.
Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily?
Answer:
The particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction is lesser in chalk, hence it could be broken easily into smaller pieces.
But the strength of inter-molecular force of attraction is very strong in coal, therefore it is not possible to break them into small pieces.