CBSE Class 12 Physics Heat and Thermodynamics Objective Questions

CBSE Class 12 Physics Heat and Thermodynamics Objective Questions. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Choose the correct option(s):

1. Two identical rectangular strips, one of copper and the other of steel, are rivetted together to form a bimetallic strip. On heating this strip, it will (αcopper > αsteel)
(a) remain straight (b) bend with copper on the convex side
(c) bend with steel on the convex side (d) get twisted

2. If I is the moment of inertia of solid body, the change in I corresponding to a small change in temperature ΔT is
(a) αI ΔT (b) 1/2 αI ΔT (c) 2 αI ΔT (d) 3 αI ΔT

3. The length of the steel rod which would have the same difference in length with a copper rod of length 16 cm at all temperature (αcopper = 18 × 10^–6 K^–1, αsteel = 12 × 10^–6 K^–1) is
(a) 20 cm (b) 18 cm (c) 24 cm (d) 30 cm

4. The density of a solid at 0°C and 500°C is in the ratio 1.027 : 1. The coefficient of linear expansion of the solid is
(a) 20 × 10^–6 K^–1 (b) 12 × 10^–6 K^–1 (c) 18 × 10^–6 K^–1 (d) 24 × 10^–6 K^–1

5. At 4°C, 98% of the volume of a body is immersed in water. The temperature at which the entire body gets immersed in water (γω = 3.3 × 10^–4 K^–1) is (neglect the expansion of the body)
(a) 40.8° C (b) 64.6° C (c) 60.0°C (d) 58.8°C

6. If α is the coefficient of linear expansion, the change in the period t of a physical pendulum with a temperature change of ΔT is
(a) 1/2 αtΔT (b) 1/4 αtΔT (c) 3/4 αtΔT (d) 1/3 αtΔT

7. Which one of the following expressions (notations having their usual meanings) does not represent ideal gas behaviour?
(a) p = ρrT (b) pV = (m/M)RT (c) pV =(m/M)rT (d) p = nkT

8. The volume V versus temperature T graphs for a certain amount of a perfect gas at two pressures p₁ and p₂ are shown in the figure here.

(a) p1 < p2 (b) p1 = p2 (c) p1 > p2 (d) It cannot be ascertained.

9. The molar heat capacity of an ideal gas at constant volume is given by
(a) γ−Ρ/ γ-1   (b) R/ γ-1  (c) γR (d) (γ – 1)R

10. The work done by a gas in an adiabatic process is
(a) P₁V₁-p₂V₂/γ-1 (b) P₂V₂-p₁V₁/γ-1  (c) R(T₁-T₂)/ γ-1 (d) nR(T₂-T₁)/ γ-1 

11. An ideal gas is compressed isothermally. The compression agent does 36 joules of work. The amount of heat that flows out from the gas is
(a) zero (b) +36 J (c) – 36 J (d) infinite

12. In an isobaric (constant pressure) process
(a) Δ Q : Δ U = 1 : 1  (b) Δ Q : Δ U = 1 : γ = 1  (c) Δ Q : Δ U = γ – 1 : 1  (d) Δ Q : Δ U = γ : 1

13. In an isobaric process
(a) Δ Q : Δ W = 1 : 1 (b) Δ Q : Δ W = γ : γ – 1  (c) Δ Q : Δ W = γ – 1 : γ  (d) Δ Q : Δ W = γ : 1

14. The internal energy of a mole of air (γ = 7/5) in a room of volume V = 40 m³ at 1 atmospheric pressure (= 105 N m^–2) is
(a) 10⁵ J (b) 10⁴ J (c) 10⁷ J (d) 10⁸ J

15. In an isobaric process
(a) the heat added is γ −1/γtimes the work done by the gas (b) the work done is zero

(c) the heat added is (γ –1) times the work done (d) the heat added has no relation with the work done

16. For an adiabatic compression, the quantity PV
(a) increases (b) decreases
(c) remains constant (d) may either increase or decrease

17. Q calories of heat is required to raise the temperature of 1 mole of a monoatomic gas from 20°C to 30°C. The amount of heat required to raise the temperature of diatomic gas from 20° C to 25° C is
(a) Q (b) 3Q/2 (c) 5Q/3 (d) 7Q/3

18. The heat capacity of an ideal gas in a polytropic process is C = C_V + 0 .1 R. The value of the polytropic exponent is
(a) 11 (b) 10 (c) – 10 (d) –9

19. An ideal gas expands according to the law pV² = constant. The molar heat capacity C is
(a) C_V + R (b) C_V – R (c) C_V + 2R (d) C_V – 3R

20. If W₁ is the work done in compressing an ideal gas from a given initial state through a certain volume isothermally and W₂ is the work done in compressing the same gas from the same initial state through the same volume adiabatically, then
(a) W₁ = W₂ (b) W₁ < W₂ (c) W₁ > W₂ (d) W₁ = 2 W₂

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