Unit – 8 : Heat and Thermodynamics (Multiple Choice Questions)

1. In hot summer after a bath, the body’s

a) internal energy decreases
b) internal energy increases
c) heat decreases
d) no change in internal energy and heat
Answer: a)

2. The graph between volume and temperature in Charles’ law is

a) an ellipse
b) a circle
c) a straight line
d) a parabola
Answer: c)

3. When a cycle tyre suddenly bursts, the air inside the tyre expands. This process is

a) isothermal
b) adiabatic
c) isobaric
d) isochoric
Answer: b)

4. An ideal gas passes from state $(P_1,V_1,T_1,N)$ to $(2P_1,3V_1,T_2,N)$. Then

a) $T_1=T_2$
b) $T_1=\dfrac{T_2}{6}$
c) $T_1=6T_2$
d) $T_1=3T_2$
Answer: b)

5. When a uniform rod is heated, which quantity increases?

a) mass
b) weight
c) centre of mass
d) moment of inertia
Answer: d)

6. When food is cooked in a vessel with lid closed, steam pushes the lid outward. Considering steam as the system

a) $Q>0, W>0$
b) $Q<0, W>0$
c) $Q>0, W<0$
d) $Q<0, W<0$
Answer: a)

7. When you exercise in the morning, considering your body as a thermodynamic system, which is true?

a) $\Delta U>0, W>0$
b) $\Delta U<0, W>0$
c) $\Delta U<0, W<0$
d) $\Delta U=0, W>0$
Answer: b)

8. A hot cup of coffee attains thermal equilibrium with surroundings. Considering air molecules as system

a) $\Delta U>0, Q=0$
b) $\Delta U>0, W<0$
c) $\Delta U>0, Q>0$
d) $\Delta U=0, Q>0$
Answer: c)

9. An ideal gas is taken from $(P_1,V_1)$ to $(P_2,V_2)$ by three different ways. Identify the process in which work done is maximum.

PV diagram showing Process A, B and C
a) Process A
b) Process B
c) Process C
d) Equal work in all
Answer: b)

10. The V–T diagram of an ideal gas undergoing reversible cycle A→B→C→D is shown. The corresponding P–V diagram is

VT diagram and PV diagram options
a) a
b) b
c) c
d) d
Answer: a)

11. A distant star emits radiation with maximum intensity at 350 nm. The temperature of the star is

a) 8280 K
b) 5000 K
c) 7260 K
d) 9044 K
Answer: a)

12. Identify the state variables

a) $Q,T,W$
b) $P,T,U$
c) $Q,W$
d) $P,T,Q$
Answer: b)

13. In an isochoric process

a) $W=0$
b) $Q=0$
c) $\Delta U=0$
d) $\Delta T=0$
Answer: a)

14. The efficiency of a heat engine operating between 0°C and 100°C is

a) 6.25%
b) 20%
c) 26.8%
d) 12.5%
Answer: c)

15. An ideal refrigerator has COP = 5 and freezer temperature −12°C. The air temperature is

a) 50°C
b) 45.2°C
c) 40.2°C
d) 37.5°C
Answer: c)