# Samacheer Kalvi 10th Science Solutions Chapter 3 Pdf

## Samacheer Kalvi 10th Science Solutions Chapter 3 Pdf

Tamilnadu Board Samacheer Kalvi 10th Science Solutions Chapter 3: Tamilnadu State Board Solution Class 10 Science Chapter 3 – THERMAL PHYSICS .

### Samacheer Kalvi 10th Science Solutions Chapter 3: Overview

 Board Samacheer Kalvi Class 10 Subject Science Chapter 3 Chapter Name THERMAL PHYSICS

### Samacheer Kalvi 10th Science Solutions Chapter 3 Pdf

#### Thermal physics

Exercise:

1) The value of universal gas constant

• a) 3.81 Jmol–1 K–1
• b) 8.03 Jmol–1 K–1
• c) 1.38 Jmol–1 K–1
• d) 8.31 Jmol–1 K–1

Ans: d ) 8.31 Jmol–1 K–1

2) If a substance is heated or cooled, the change in mass of that substance is

• a) positive
• b) Negative
• c) Zero
• d) None of the above

Ans: c) Zero

Because, there is no effect of temperature on the mass of the substance because also mass is conserved during this process.

3) If a substance is heated or cooled, the linear expansion occurs along the axis of

• a) X or –X
• b) Y or –Y
• c) Both (a) and (b)
• d) (a) or (b)

Ans: a) X or –X

Because, in linear expansion the length of the object changes only.

4) Temperature is the average ___________ of the molecules of a substance

• a) Difference in K.E and P.E
• b) Sum of P.E and K.E
• c) Difference in T.E and P.E
• d) Difference in K.E and T.E

Ans: c) Difference in T.E and P.E

Because, the total energy is the sum of potential and kinetic energy. And temperature is the average kinetic energy of the molecules.

Hence, T.E. = K.E. + P.E.

K.E, = T.E. – P.E.

5) In the Given diagram, the possible direction of heat energy transformation is

Ans: a) A←B, A←C, B ←C.

Because, temperature always flows from region of higher temperature to region of lower temperature.

Fill in the blanks:

1) The value of Avogadro number ________

Ans: The value of Avogadro number 6.023*1023/mole

2) The temperature and heat are _________ quantities

Ans: The temperature and heat are scalar quantities

3) One calorie is the amount of heat energy required to raise the temperature of _______ of water through______.

Ans: One calorie is the amount of heat energy required to raise the temperature of one gram of water through10C.

4) According to Boyle’s law, the shape of the graph between pressure and reciprocal of volume is ________________

Ans: According to Boyle’s law, the shape of the graph between pressure and reciprocal of volume is straight line.

III. State whether the following statements are true or false, if false explain why?

1) For a given heat in liquid, the apparent expansion is more than that of real expansion.

Ans: False

Correct statement: For a given heat in liquid, the real expansion is more than the apparent expansion.

2) Thermal energy always flows from a system at higher temperature to a system at lower temperature.

Ans: True

3) According to Charles’s law, at constant pressure, the temperature is inversely proportional to volume.

Ans: False

Correct statement: According to Charles’s law, at constant pressure the volume of gas is directly proportional to the absolute temperature.

IV. Match the items in column-I to the items in column-II

Ans:

• Linear expansion: change in length
• Superficial expansion: change in the area
• Cubical expansion: change in volume
• Heat transformation: hot body to cold body
• Boltzmann constant: 1.382*10-23 JK-1

V. Assertion and reason type questions

A> Both the assertion and the reason are true and the reason is the correct explanation of the assertion.

B> Both the assertion and the reason are true but the reason is not the correct explanation of the assertion.

C> Assertion is true but the reason is false.

D> Assertion is false but the reason is true.

1. Assertion: There is no effects on other end when one end of the rod is only heated.

Reason: Heat always flows from a region of lower temperature to higher temperature of the rod.

Ans: c. Assertion is true but the reason is false.

Because, heat always flows from higher temperature to lower temperature.

2.Assertion: Gas is highly compressible than solid and liquid

Reason: Interatomic or intermolecular distance in the gas is comparably high.

Ans: b. both the assertion and the reason are true but the reason is not the correct explanation of the assertion.

1) Define one calorie.

Ans: One calorie:

It is the amount of energy which is required to raise the temperature of one gram of water through 10C.

2) Distinguish between linear, arial and superficial expansion.

Ans: Linear expansion:

• When the length of the body changes due to change in its temperature which is caused due to heating or cooling of body, this type of expansion is called as linear or longitudinal expansion.
• The ratio of increase in length of the body per degree rise in temperature to its unit length is called as coefficient of linear expansion and it is different for different materials.
• The SI unit of coefficient of linear expansion is K-1.

Arial or superficial expansion:

• If the solid object is heated then its area get increased, this increase in area of solid object due to heating is called as areal or superficial expansion.
• The ratio of increase in area of the body per degree rise in temperature to its unit area is called as coefficient of superficial expansion and its value is different for different materials.
• The SI unit of coefficient of superficial expansion is K-1.

Cubical expansion:

• If the solid object is heated then its volume get increased, this increase in volume of the solid object due to heating is called as cubical expansion.
• The ratio of increase in volume of the body per degree rise in temperature to its unit volume is called as coefficient of cubical expansion and its value is different for different materials.
• The SI unit of cubical expansion is K-1.

3) What is co-efficient of cubical expansion?

Ans: Coefficient of cubical expansion:

The ratio of increase in volume of the body per degree rise in temperature to its unit volume is called as coefficient of cubical expansion and its value is different for different materials.

The SI unit of cubical expansion is K-1.

4) State Boyle’s law

Ans: Boyle’s law:

When the temperature of the body is constant, the volume of the fixed amount of gas is inversely proportional to its pressure.

It is given by,

At constant temperature, P α 1/V.

5) State-the law of volume

Ans: The law of volume:

Charles’s law is also known as the law of volume.

According to this law, at a constant pressure the volume of a gas is directly proportional to the temperature of the gas.

It is given by, V α T.

6) Distinguish between ideal gas and real gas.

Ans:

Ideal gas:

• If the molecules of gas are not interacting with each other then that gas is said to be ideal gas or a perfect gas. But such gas not exist practically.
• The real gas at low pressure or high temperature can be called as ideal gas, because at high temperature there is no interatomic force of attraction between the gas molecules.

Real gas:

• If the molecules or atoms of a gas are interacting with each other with a intermolecular force of attraction the that gas is called as real gas.
• At high temperature or low pressure there is a weak force of intermolecular attraction in between molecules of the real gas and hence it acts as a ideal gas.

7) What is co-efficient of real expansion?

Ans: Coefficient of real expansion:

The ratio of the true rise in the volume of the liquid per degree rise in temperature to its unit volume is called as coefficient of real expansion.

The SI unit of coefficient of real expansion is K-1.

8) What is co-efficient of apparant expansion?

Ans: Coefficient of apparent expansion:

The ratio of the apparent rise in the volume of the liquid per degree rise in the temperature to its unit volume is called as coefficient of apparent expansion.

The SI unit of coefficient of apparent expansion is K-1.

VII. Numerical problems

1) Find the final temperature of a copper rod. Whose area of cross section changes from 10 m2 to 11 m2 due to heating? The copper rod is initially kept at 90 K. (Coefficient of superficial expansion is 0.0021 /K)

Ans:

Given that,

Area of copper rod before heating A1 = 1O m2

Area of copper rod after heating A2 = 11 m2

Hence, change in area of copper rod ∆A= A2 – A1 = 11 – 10 = 1 m2

Initial temperature of copper rod is T1 = 90 K

Hence, change in temperature of copper rod ∆T = T2 – T1 = T2 – 90

Also, coefficient of superficial expansion is αA = 0.0021 K-1.

The relation for superficial expansion is given by,

αA* ∆T = ∆A/ A1

∆T = ∆A/ (αA*A1)

T2 – 90 = 1/ (0.0021*10)

T2 – 90 = 1/ 0.021

T2 – 90 =47.61

T2 = 47.61 + 90 = 137.61K

Thus, the final temperature of the copper rod will be 137.61 K.

2) Calculate the coefficient of cubical expansion of a zinc bar. Whose volume is increased 0.25 m3 from 0.3 m3 due to the change in its temperature of 50 K.?

Ans:

Give that, initial volume V1 = 0.25 m3

Final volume V2 = 0.3 m3

Hence, change in volume ∆V = V2 – V1 = 0.3 – 0.25 = 0.05 m3

Change in temperature ∆T = 50 K

For cubical expansion,

αV* ∆T = ∆V/ V1

αV= (∆V/ V1*∆T)

= 0.05/ 0.25*50 = 0.004 K-1.

Thus, the coefficient of cubical expansion of a zinc bar is 0.004K-1.

1) Derive the ideal gas equation.

Ans: If the molecules of gas are not interacting with each other then that gas is said to be ideal gas or a perfect gas.

An ideal gas obeys Boyle’s law, Charles’s law and Avogadro’s law.

By Bayle’s law,

PV = constant

By Charles’s law,

V/T = constant

V/n = constant

By combining above three equations we get,

PV/nT = constant

The above equation is called as combined law of gases.

Let us consider the gas containing μ moles and number of atoms equal to μ times the Avogadro’s number NA,

Hence we write as, n = μNA

Then we get as,   PV / μNAT = constant

In the above equation the constant is taken as kB which is called as Boltzmann constant and having value as 1.38* 10-23 JK-1.

We rewrite it as, PV / μNAT = kB

PV = μNAT*kB

PV = μNAkBT

Since, μNAkB = R, which is called as the Universal gas constant and its value is 8.314 J k-1mol-1.

Thus,   PV = RT

The above equation is called as ideal gas equation or equation of state also as it gives the relation between state variables and also used for describing the state of any gas.

2) Explain the experiment of measuring the real and apparent expansion of a liquid with a neat diagram.

Ans: Experimental explanation of measuring real and apparent expansion of a liquid:

• The liquid whose real and apparent expansion has to be measured is poured in a container up to a level and mark it as L1. Now, we heat the liquid by heating the container with the help of burner as shown in figure.

Fig. Real and apparent expansion of liquid

• Initially due to thermal energy gaining the liquid starts to expand. Due to this expansion the volume of liquid get decreased and note that level and mark it as L2.
• In similar way, if we further heated that liquid it expands and there is decrease in its volume. Note that level and mark it as L3.
• The difference between the level L1 and L3 is called as apparent expansion.
• And the difference between the levels L2 and L3 is called as real expansion.
• And always the real expansion is more than that of apparent expansion.

Hence we can write as,

• Real expansion = L3 – L2
• Apparent expansion = L3 – L1

HOT question

1) If you keep ice at 0°C and water at 0°C in either of your hands, in which hand you will feel more chillness? Why?

Ans:

When we keep ice at 00C and water at 00C in either of our hands then the hand with ice feels more chillness. Because, ice get melted by taking heat energy from hand and more amount of energy is transferred due to latent heat of fusion. Hence the hand with ice feels more chillness

Updated: June 30, 2021 — 1:26 pm