Question 1

Question 3Fill in the blanks:(a) Boiling occurs at ............... .(b) Evaporation takes place at ............... .(c) The molecules of liquid ............... heat from surroundings in evaporation.(d) Heat is ............... during boiling.(e) Cooling is produced in ............... .(f) A longer rod expands ............... than a shorter rod on being heated to the same temperature.(g) Liquids expand ............... than the solids.(h) Gases expand ............... than the liquids.(i) Alcohol expands ............... than water.(j) Iron expands ............... than copper.

Accepted Answer

(a) Boiling occurs at a fixed temperature.(b) Evaporation takes place at all temperatures.(c) The molecules of liquid absorb heat from surroundings in evaporation.(d) Heat is absorbed during boiling.(e) Cooling is produced in evaporation.(f) A longer rod expands more than a shorter rod on being heated to the same temperature.(g) Liquids expand more than the solids.(h) Gases expand more than the liquids.(i) Alcohol expands more than water.(j) Iron expands less than copper.

Question 2

Question 2Distinguish between liquid and vapour (or gas) states of matter on the basis of the following factors:(a) Arrangement of molecules(b) Inter-molecular separation(c) Inter-molecular force and(d) Kinetic energy of molecules

Accepted Answer

PropertyLiquidsGasesArrangement of moleculesMolecules are not rigid and they are less closely packedMolecules are very loosely packedInter-molecular separationThe inter-molecular spaces are more than solidsThe inter-molecular space is very large as compared to solids and liquidsInter-molecular forceThe force is weak and molecules are free to move within the boundary of the containerThe force is very weak so molecules are free to move anywhereKinetic energy of moleculesThe kinetic energy is more than solidsKinetic energy is the most in gases.

Question 3

Question 3What is evaporation? Explain it on the basis of molecular motion.

Accepted Answer

The change of liquid into its vapour at all temperatures from its surface is called evaporation.The inter-molecular force of attraction is lesser in liquids as compared to solids. Hence, liquid molecules can move throughout the liquid and in the process they collide with each other transferring energy between them. Molecules with higher kinetic energy reach the surface of the liquid while those with lesser kinetic energy remain inside the liquid. The higher energy molecules on the surface absorb some more heat from the surroundings to gain sufficient kinetic energy to do work against the force of attraction on them due to other molecules inside the liquid and escape out from the surface into space. These escaping molecules form the vapour of the liquid. The process continues till all the liquid evaporates.

Question 4

Question 5Describe an experiment to demonstrate the thermal expansion in solids.

Accepted Answer

The thermal expansion in solids can be demonstrated by the following experiment:Take a ball and ring set-up as shown in figure. It consists of a metal ball and a ring. The metal ball just slips through the ring when both are at room temperatureNow heat the ball on a burner and place it over the ring. We will observe that the ball does not pass through the ring.Now allow the ball to cool by itself and after some time again place it over the ring. We will observe that the ball passes through the ring.Conclusion — On heating the ball expands and becomes bigger than the diameter of the ring so it does not pass through the ring. But on cooling the ball contracts and passes through the ring.

Question 5

Question 6Describe an experiment to show that liquids expand on heating.

Accepted Answer

The following experiment demonstrates that liquids expand on heating:Take an empty bottle with a tight fitting cork with a hole drilled in its middle, a drinking straw, two bricks, a wire gauze and a burner.Fill the bottle completely with water. Add few drops of ink to make it coloured for easy contrast.Fix the cork in the mouth of the bottle. Pass the drinking straw through the cork. Put some molten wax around the hole to avoid leakage of water.Pour some more water in the drinking straw so that water level in the straw can be seen. Mark the water level in the straw as shown in figure.Place the bottle on the wire gauze kept over the two bricks. Heat the bottle using a burner as shown in figure.Look at the level of water in the straw.When water is heated more and more, the level of water in the drinking straw rises. This shows that water expands on heating.

Question 6

Question 7Describe an experiment to show that air expands on heating.

Accepted Answer

The following experiment demonstrates that air expands on heating:Take an empty bottle. The empty bottle contains air.Attach a rubber balloon to its neck as shown in figure.The balloon is deflated initially.Place the bottle in a water bath containing boiling water. It heats the air present in bottle.After sometime it is noticed that the balloon gets inflated as shown in figure.Conclusion — This shows that on heating, air present inside bottle expands and fills the balloon. So the balloon gets inflated. This shows that air expands on heating.

Question 7

Question 8Describe an experiment to show that same volume of different liquids heated to same rise in temperature expand by different amounts.

Accepted Answer

The following experiment demonstrates that same volume of different liquids heated to same rise in temperature expand by different amounts:Take four identical glass bottles each fitted with a narrow glass tube through a cork at its mouth.Fill them up to the same level with different liquids like water, alcohol, kerosene, benzene.Place them in a common water bath containing boiling water as shown in figure.Observations — After sometime it is noticed that different liquids rise to different levels. Benzene expands the most followed by alcohol and kerosene. Water expands the least.Conclusion — From the above experiment it is concluded that, same volume of different liquids heated to same rise in temperature expand by different amounts.

Question 8

Question 1(i)The correct statement is:Iron rims are cooled before they are placed on the cart wheels.A glass stopper gets tightened 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.

Accepted Answer

A little space is left between two rails on a railway trackReason — During summer season due to rise in temperature the rails expands, so little space is left between two rails on a railway track, otherwise the rails will bend sideways.

Question 9

Question 4Comment on the statement 'Evaporation is a surface phenomenon'.

Accepted Answer

Due to weak inter-molecular force of attraction the molecules of a liquid move freely inside it. In the process, they collide with each other transferring energy between them. Molecules with higher kinetic energy reach the surface of the liquid while those with lesser kinetic energy remain inside the liquid. The higher energy molecules on the surface absorb some more heat from the surroundings to gain sufficient kinetic energy to do work against the force of attraction on them due to other molecules inside the liquid and escape out from the surface into space. These escaping molecules form the vapour of the liquid. Thus, evaporation of the liquid happens only from the surface of the liquid. Hence, Evaporation is a surface phenomenon.

Question 10

Question 11State three factors on which depend the linear expansion of a metal rod on heating.

Accepted Answer

The three factors on which the linear expansion of a metal rod on heating depends are:Original length of the rodIncrease in temperatureMaterial of the rod

Question 11

Question 12A metal plate is heated. State three factors on which the increase in its area will depend.

Accepted Answer

The increase in area of a metal plate depends on following three factors:The initial area of the plate.The increase in temperature.Material of the plate.

Question 12

Question 16100 ml of each of the following liquids is heated from 10°C to 50°C. Which will expand more:(a) water(b) benzene(c) alcohol?

Accepted Answer

Benzene will expand more than alcohol and water because expansion of a liquid depends upon the nature of liquid since volume and temperature are same. Coefficient of cubical expansion of benzene is more than alcohol and water. So it expands the most.

Question 13

Question 17Water is heated from 0°C to 4°C. Will it expand?

Accepted Answer

No, water will not expand. Water contracts on heating it from 0°C to 4°C. On heating beyond 4°C it expands.

Question 14

Question 18What do you mean by anomalous behavior of water?

Accepted Answer

Water contracts on heating it from 0°C to 4°C and then beyond 4°C on further heating, it expands. This is called anomalous behavior of water.

Question 15

Question 19How does the density of a substance (solid, liquid and gas) change on heating?

Accepted Answer

When a substance is heated, its volume increases while its mass remains same. So density of substance decreases with increase in temperature.In case of solids, when temperature increases, increase in volume is negligible so decrease in density is not appreciable.But in case of liquids and gases as temperature increases, volume increases by an appreciable amount, so density decreases considerably.

Question 16

Question 8(c)Explain the following:Gaps are left between the successive rails on a railway track.

Accepted Answer

In summer season due to rise in temperature, each rail expands in length. By leaving a gap between the two rails, the rails get a chance to expand in this space. This prevents the rails from bending sideways and derailing the train.

Question 17

Question 9Why is one end of a steel girder in a bridge kept on rollers instead of fixing it in a pillar?

Accepted Answer

One end of a steel girder in a bridge is kept on rollers instead of fixing it in a pillar because in summer or in winter when there is rise or fall in temperature, the girder may expand or contract without affecting the pillar or bridge.

Question 18

Question 10An 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 water. Explain the reason.

Accepted Answer

The empty glass bottle is filled with air. When the bottle is heated, the air inside the bottle expands and it escapes out through the tube into water in the form of bubbles.

Question 19

Question 11An iron washer is heated. State the effect on its:(a) mass(b) internal diameter(c) external diameter and(d) density.

Accepted Answer

(a) Mass does not change on heating.(b) When iron washer is heated, it expands so internal diameter increases.(c) External diameter increases as iron washer expands on heating.(d) Density decreases as volume of the iron washer increases on heating.

Heat Transfer

Exercise 6 Fill In The Blanks

Exercise 6 Long Answer Type Questions

Exercise 6 Objective Type Questions

Exercise 6 Short Answer Type Questions

Exercise 6 Think And Answer