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# Multiple Choice Questions - Physics: Heat and Thermodynamics

1 mark question and answers, Multiple Choice Questions - Physics: Heat and Thermodynamics - Physics : Heat and Thermodynamics

Heat and Thermodynamics (Physics)

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) internal energy decreases

Solution : Temperature decreases, So internal energy decreases.

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) a straight line

Solution: P - constant, VT

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

a) isothermal

c) isobaric

d) isochoric

4. An ideal gas passes from one equilibrium state (P1V1T1N) to another equilibrium state (2P1, 3V1T2N). Then

a) T1=T2

b) T1=T2/6

c) T1=6T2

d) T1=3T2

Answer: b) T1 = T2 / 6

Solution:

T1 = T2 / 6

2P1 3V1 = NKT2

6P1V1 = NKT2

P1V1 = NKT2 / 6

NKT1 = NK T2 / 6

P1V1 = NKT1

NKT1 = NK T2 / 6

T1 = T2 / 6

5. When a uniform rod is heated, which of the following quantity of the rod will increase

a) mass

b) weight

c) center of mass

d) moment of inertia

Answer : d) moment of inertia

Solution:

I = mr2

Due to thermal expansion, if T increases I also increases.

6. When food is cooked in a vessel by keeping the lid closed, after some time the steam pushes the lid outward. By considering the steam as a thermodynamic system, then in the cooking process

a) Q > 0, W > 0,

b) Q < 0, W > 0,

c) Q > 0, W < 0,

d) Q < 0, W < 0,

Solution:

Heat is given to the system

System gains heat → Q > 0

Lid Pushes upwards → Work done

by the system → W > 0

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

a) U > 0, W > 0,

b) U < 0, W > 0,

c) U < 0, W < 0,

d) U = 0, W > 0,

Answer : b) ΔU < 0, W > 0,

Solution:

Workdone by the system, W > 0

Heat flows outward → ΔU ↓

8. A hot cup of coffee is kept on the table. After some time it attains a thermal equilibrium with the surroundings. By considering the air molecules in the room as a thermodynamic system, which of the following is true

a) U > 0, Q = 0

b) U > 0, W < 0

c) U > 0, Q > 0

d) U = 0, Q > 0

Answer : c) ΔU > 0, Q > 0

9. An ideal gas is taken from (Pi,Vi) to (Pf,Vf) in three different ways. Identify the process in which the work done on the gas the most. a) Process A

b)Process B

c) Process C

d) Equal work is done in Process A,B &C

10. The V-T diagram of an ideal gas which goes through a reversible cycle A→B→C→D is shown below. (Processes D→A and B→C are adiabatic) The corresponding PV diagram for the process is (all figures are schematic) Ans: b

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

a) 8280 K

b) 5000K

c) 7260 K

d) 9044 K

Solution:

λm = b / T

T = b / λm

= 2.898×10-3 / 350×10-9

λm = 8280 K

12. Identify the state variables given here?

a) Q, T, W

b) P, T, U

c) Q, W

d) P, T, Q

Answer : b) P, T, U

13. In an isochoric process, we have

a) W = 0

b) Q = 0

c) ∆U = 0

d) ∆T = 0

14. The efficiency of a heat engine working between the freezing point and boiling point of water is

a) 6.25%

b) 20%

c) 26.8%

d) 12.5%

Solution:

Tn = 100°C

Tn = 373

TL = 0°C

TL = 273 K

[ TH − TL ] / TH = n

= ( [373 – 273] / 373 ) × 100

= ( 100 / 373 ) × 100

n = 26.8%,

15. An ideal refrigerator has a freezer at temperature −12°C. The coefficient of performance of the engine is 5. The temperature of the air (to which the heat ejected) is

(a) 50°C

(b) 45.2°C

(c) 40.2°C

(d)37.5°C

Solution:

TL = −12°C + 278 K

TL = 261 K,

B=5,

TH = ?

β = TL / [TH – TL ]

TH = [ TL β ] + TL

= [261/5] + 261

= 525 + 261

= 313.2K

TH = 313.2 K − 273°C

TH = 40.2°C

1) a     2) c    3) b   4) b

5) d   6) a    7) b   8) c

9) b 10) b 11) a  12) b

13) a  14) b 15) c

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11th Physics : Heat and Thermodynamics : Multiple Choice Questions - Physics: Heat and Thermodynamics |

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