Chapter 4 – Thermal phenomena

Physical Science

Book Name	: Physical Science and Environment
Subject	: Physical Science
Class	: 10 (Madhyamik)
Publisher	: Oriental Book Company Private Limited
Chapter Name	: Thermal Phenomenon

Table of Contents

Short Answer Type Questions :

Question – 1

What is the linear expansion of a solid ?

Answer

The increase of length of a solid substance with the increase in temperature is known as linear expansion of a solid.

Question – 2

Name the three types of expansion in solid ?

Answer

The types of expansion in solid are:

Linear expansion,
Areal expansion or superficial expansion, and
Volume expansion.

Question – 3

Name a substance which contracts on heating.

Answer

Rubber.

Question – 4

Define the term ‘coefficient’ of linear expansion.

Answer

The coefficient of linear expansion of a solid is the increase in its length per unit length per degree rise of temperature.

Question – 5

Give SI unit of coefficient of linear expansion.

Answer

Kelvin^-1 (K^-1).

Question – 6

Is the coefficient of linear expansion possible in the case of liquid?

Answer

No, because the liquid has no definite length.

Question – 7

The coefficient of linear expansion of brass in 1.8 x 10^-5C^-1. What do you mean by this?

Answer

This means 1 cm of a brass rod (at 0^oC) expands linearly by 1.2×10^-5 cm for 1^oC rise in temperature.

Question – 8

Write the relationship between α β, and γ.

Answer

α=β/2=γ/3

Question – 9

Does the unit of coefficient of linear expansion depend on the unit of length?

Answer

Since the coefficient of linear expansion is the ratio of length, its unit does not depend on length. It only depends on the temperature.

Question – 10

Is linear expansion possible in the case of liquids? Explain.

Answer

No, because the liquid has no definite length.

Question – 11

Why there is an apparent expansion in liquids?

Answer

There is an apparent expansion in liquids because when a liquid contained in a solid container is heated, the solid container undergoes expansion along with the liquid.

Question – 12

Why there is no apparent expansion in gases?

Answer

For the rise of temperature, the expansion of gas is very high as compared to the container. So the expansion of the vessel can be neglected in the case of gases and no apparent expansion in gases is considered.

Question – 13

What is thermal conduction?

Answer

The process of transfer of heat through a substance without any motion of the particles of the substances is called thermal conduction.

Question – 14

Name two substances which are good conductors of heat.

Answer

Aluminium and copper.

Question – 15

Name two bad conductors of heat.

Answer

Wood and glass.

Question – 16

What is the S.I. unit of thermal conductivity?

Answer

J/m/K/s

Short Answer Type Questions :

Question – 17

Explain why are there gaps between the rails.

Answer

A gap is maintained between the successive lengths of rail to provide space for the expansion rail on hotter days due to a rise in temperature. Otherwise, the rails are likely to buckle and accidents may occur.

Question – 18

Why is a glass chimney cracked when water drops fall on it.

Answer

When a drop of water falls on a hot glass chimney there is a sudden drop of temperature on the spot where the water drop hits. This decrease in temperature makes the glass to contract. The stress developed on the site of contraction is responsible for the cracking of the glass chimney.

Question – 19

Explain an experiment to show that different metals expand by a different amount.

Answer

For this simple experiment, a composite bimetallic strip is taken consisting of two flat bars of different metals (A.B.) revetted or welded together. When heated the straight bar is found to bend as shown in fig (b). Metal A expands more than metal B, but as they are joined together, they can not expand independently, the strip bends with the more expanding metal bar (A) on the convex side. This experiment proves that different metals expand by different amounts.

Question – 20

Describe an experiment to show that solids expand on heating and contract on cooling.

Answer

Experiment: Cubic expansion of an iron ball on heating

Take an iron ball and a ring such that the ball just passes through the ring as shown in fig (a). Now, heat the ball and try to pass it through the ring. You will find that the ball does not pass through the ring fig (b). Why is this so?

When the ball is heated, it expands and its size increases. After some time, when the ball coos, it will again pass through the ring. This experiment shows that solids expand on heating and contract on cooling.

Question – 21

Define the coefficient of linear expansion of a solid. Give its mathematical expression. Mention its units.

Answer

Coefficient of linear expansion: The coefficient of linear expansion of a solid is the increase in its length per unit length per degree rise of temperature.

The mathematical expression of the coefficient of linear expansion:

α= $l_2−l_1\over l_1(t_2−t_1)$

l₁ = Initial length

l₂ = Final length

t₁ = Initial Temperature

t₂ = Final Temperature

Unit of the coefficient of linear expansion:

It is expressed as per degree Celcius (^oC^-1) or per degree kelvin (K^-1)

Question – 22

Describe an experiment to show that liquids expand on heating.

Answer

Aim: To show that liquid expands on heating

Things Required: An empty bottle, cork having a hole drilled, a drinking straw, wire gauze, tripod stand, burner

Procedure: Take a bottle fill it completely with water and add drops of ink to it to make it coloured.

Fix the cork in the mouth of the bottle and pass the drinking straw through the cork. Put some molten wax around the hole to avoid the leakage of water.

Pour some more water into the drinking straw so that the water level in the straw can be seen.

Question – 23

Why are there two types of expansion in liquids?

Answer

There are two types of expansion of a liquid because when a liquid contained in a solid container is heated, the solid container undergoes expansion along with the liquid.

Question – 24

Give an example to show that gases expand on heating. Gases are kept in some vessels for measurement, still, why is there an apparent expansion of gases?

Answer

An air-filled balloon made of this rubber, when kept outside under the sun, is found to become larger in size and ultimately burst out. This shows that air on being heated expands in volume.

Question – 25

State Charles’ law. Give its mathematical form.

Answer

Charle’s law: At constant pressure, the volume of a given mass of a gas increases or decreases by 1/273 of its volume at 0°C for each one-degree rise or fall in temperature.

The mathematical form of Charle’s law:

V_t=V_o(1+t/273)

V_o = volume at 0°C

V_t = volume at t°C

Question – 26

Describe an experiment to show that heat is conducted through a metal rod. Is there any material movement of the rod?

Answer

Experiment

Take a rod or flat strip of metal. Fix a few small wax pieces on the rod. These pieces should be at nearly equal distances. Clam the rod to a stand or place one end of the rod in between two bricks. Heat the other end of the rod with a candle.

Observation

The heat from the candle side passes towards the other end by dissolving wax pieces on the rod.

Conclusion

This experiment shows that heat is transferred from the hotter end to the colder end.

There is no material movement of the rod.

Question – 27

What do you mean by good and bad conductors? Give some examples.

Answer

Good conductors are those substances through which heat is easily conducted

Example: iron, copper

Bad conductors are those substances through which heat is not conducted easily

Example: wood, cloth

Question – 28

Describe some experiments to demonstrate the thermal expansion of a solid.

Answer

To show – Thermal expansion in solids

Experiment

Gravesand’s ball and ring experiment

Take a metallic ball and ring such that the ball can pass through the ring easily. The ball is heated, and the ball cannot pass through the ring.

This is because the solid ball expands in size. On cooling, it can pass through the ring.

Observation

Solids expand on heating and contract on cooling.

Long Answer Type Questions

Question – 29

Define coefficients of real and apparent expansions of a liquid. Give the relation between them.

Answer

Charles’ Law states that, at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.

The reason why pressure is kept constant in Charles’ Law is that the volume of a gas is highly dependent on the pressure it is subjected to. If the pressure were to change while the temperature remained constant, the volume would also change, making it difficult to establish a direct relationship between the two.

Question – 30

State and explain Charles’ law. Why is pressure kept constant here?

Answer

Charle’s law: At constant pressure, the volume of a given mass of a gas increases or decreases by 1/273 of its volume at 0°C for each one-degree rise or fall in temperature.

The mathematical form of Charle’s law:

V_t=V_o(1+t/273)

V_o = volume at 0°C

V_t = volume at t°C

Pressure is kept constant in Charles’ law to isolate the effect of temperature on the volume of a gas, ensuring changes in volume are directly proportional to changes in temperature.

Question – 31

What do you mean by good and bad conductors? Give some examples of each. State coefficient of thermal expansion of a solid. What is its SI unit?

Answer

Good conductors are materials that allow heat or electricity to flow through them easily. Examples of good conductors include metals such as copper, aluminium, gold, and silver.

Bad conductors, also known as insulators, are materials that do not allow heat or electricity to flow through them easily. Examples of bad conductors include rubber, wood, plastic, and air.

The coefficient of thermal expansion is defined as the fractional increase in length or volume per unit rise in temperature.

The SI unit of the coefficient of thermal expansion is 1/K.

Objective Type Questions

Question – I

Fill in the Blanks:

The expansion of a substance on heating is called ____ expansion.
The coefficient of linear expansion of a solid does not depend on the unit of ____.
Thermal resistivity is the ____ of thermal conductivity.
In Charle’s law, a ____ mass of gas is taken.
A liquid good conductor of heat is ____

Answer

Thermal
length
reciprocal
given
Mercury

Question – II

State whether true or false.

The unit coefficient of linear expansion of a solid depends on units of length as well as temperature.
The density of water is maximum at 4°C temperature.
The thermal conductivity of the diamond is maximum.
The coefficient of linear expansion is three times the coefficient of volume expansion of a solid.
Diamond is a very good conductor of heat.

Answer

False
True
True
False
True

Question – III

Match the Following:

Column-I	Column-II
The coefficient of linear expansion A thick glass tumbler cracks, when hot water poured in it. Volume of water is minimum at conduction of heat coefficient of thermal conductivity	Wm^-1K^-1 4^oC glass in bad conductor of heat γ / 3 material medium required