X – Physics
Thermal Physics
3. THERMAL PHYSICS
Prioritized Syllabus 3.1, 3.1.1, 3.1.2, 3.2, 3.2.1, 3.2.2,
3.4, 3.4.1, 3.4.2, 3.4.3, 3.5, 3.5.1, 3.5.2
Evaluation
I
II
III
IV
V
VI
VII
VIII
IX
Choose Fill up T/F Match A&R
SA
Problems DA HOTS
2,4,5
1,2,3,4 2,3
4
1,2 1,4,5,6
1
I.
Choose the appropriate answer:
1. d 2. c 3. d 4. c 5. a
II.
Fill in the blanks:
1. 6.023×1023
2. Scalar
III.
1.
2.
3.
IV.
3. 1 gram, 1°C
4. Straight line
True or False:
False.
For a given heat in liquid, the real expansion is more than that of apparent expansion.
True.
False.
According to Charles’s law, at constant pressure, the temperature is directly proportional
to volume.
Match the following:
Column – I
Linear expansion
Superficial expansion
Cubical expansion
Heat transformation
Boltzmann constant
Column – II
Change in volume
Hot body to cold body
1.381 × 10-23 JK-1
Change in length
Change in area
Answer
Change in length
Change in area
Change in volume
Hot body to cold body
1.381 × 10-23 JK-1
V.
1.
2.
Assertion and reasoning:
Both assertion and reason are false.
(a) Both assertion and reason are true, and reason is the correct explanation for assertion.
VI.
1.
Answer Briefly:
Define one calorie.
 One calorie is defined as the amount of heat energy required to raise the
temperature of 1 gram of water through 1°C.
Distinguish between linear, areal and cubical expansion.
2.
Linear expansion
Areal expansion
Cubical expansion
The increase in length of a The increase in area of a The increase in volume of a
solid object due to heating.
solid object due to heating. solid object due to heating.
It is also called longitudinal It is also called superficial It is also called volumetric
expansion.
expansion.
expansion.
S.I unit is K-1.
3.
S.I unit is K-1.
S.I unit is K-1.
What is 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.
 Its S.I unit is K-1.
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X – Physics
4.
5.
6.
Thermal Physics
State Boyle’s law.
 At a constant temperature, the volume of a fixed mass of a as is inversely
proportional to its pressure.
 P
State the law of volume. (Charle’s law)
 At a constant pressure, the volume of a as is directly proportional to its
temperature.

Distinguish between ideal gas and real gas.
Real gas
The molecules of a gas interact with each other
with a definite amount of intermolecular force of
attraction.
At very high temperature or low pressure, it
behaves as an ideal gas.
Real gases do not obey ideal gas laws.
7.
8.
VII.
1.
Ideal gas
The molecules of a gas do not interact with
each other, the intermolecular force of
attraction is weak.
At very high temperature or low pressure, real
gas is termed as an ideal gas.
Ideal gases obey Boyle’s law, Charle’s law and
Avogadro’s law.
What is coefficient of real expansion?
 Coefficient of real expansion is defined as the ratio of the true rise in the volume of
the liquid per degree rise in temperature to its unit volume.
 Its S.I unit is K-1.
What is coefficient of apparent expansion?
 Coefficient of apparent expansion is defined as the ratio of the apparent rise in the
volume of the liquid per degree rise in temperature to its unit volume.
 Its S.I unit is K-1.
Numerical problems:
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).
 A0 = 10 m2 ; A1 = 11 m2 ; T0 = 90 K ; T1 = ? ; = 0.0021 /K
-

-

-
 T1 – 90 = 1/(0.0021×10)
 T1 = 47.6 + 90
 T1 = 137.6 K
2.
Calculate the coefficient of cubical expansion of a zinc bar, whose volume is
increased from 0.25 m3 to 0.3 m3 due to the change in its temperature of 50 K.
 V0 = 0.25 m3 ; V1 = 0.3 m3 ; ΔT = 50 K ; V = ?


–

VIII.
1.
Answer in detail:
Derive the ideal gas equation.
 The ideal gas equation relates all the properties of an ideal gas.
 It obeys Boyle’s law, Charle’s law and Avogadro’s law.
 By Boyle’s law,
PV = a constant
 By Charle’s law,
V/T = a constant
 By Avogadro’s law, V/n = a constant
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X – Physics
Thermal Physics
 From the above equations,








2.
The constant is kB = 1.38 × 10-23 JK-1 (Boltzmann constant).
The above relation is called the combined law of gases.
For µ moles of a gas, the number of atoms, n = µ × NA (Avogadro’s number)
Therefore, PV = µ NA kB T = µRT.
Where, NA kB = R is the universal gas constant. (R = 8.34 J mol-1 K-1)
PV = µRT is called the ideal gas equation.
If µ=1 mol, then PV = RT.
This equation is called the equation of state, because it is used to describe the state
of any gas and to relate the state variables.
Explain the experiment of measuring the real and apparent expansion of a liquid
with a neat diagram.
 Pour the experimental liquid in a container up to a level and mark the level as L1.
 Now heat the container with liquid using a burner.
 Initially the container expands on receiving the thermal energy and the volume of
the liquid appears to be reduced.
 Mark the reduced level of the liquid as L2.
 On further heating, the heat supplied to the system produces an expansion in the
liquid and the liquid rises to L3.
 Difference between L1 and L3 is called apparent expansion. (L3 – L1)
 Difference between L2 and L3 is called real expansion. (L3 – L2)
 The real expansion is always greater than the apparent expansion.
IX.
1.
HOT questions:
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?
 We feel more chillness in the hand with ice at 0°C.
Reason:
 The latent heat of vaporization absorbed by ice is greater than that absorbed by
water.
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