CBSE Class 11 Physics Thermodynamic MCQs

Question: First law of thermodynamics states that

• a) heat is a form of energy
• b) system has pressure
• c) system has temperature
• d) system can do work

Answer: heat is a form of energy

Question: A system X is neither in thermal equilibrium with Y nor with Z. The systems Y and Z

• a) may be in thermal equilibrium
• b) None of these
• c) cannot be in thermal equilibrium
• d) must be in thermal equilibrium

Answer: may be in thermal equilibrium

Question: Which of the following macroscopic variable is not measurable?

• a) None of these
• b) Volume
• c) Pressure
• d) Mass

Answer: None of these

Question: Which of the following is a state variable ?

• a) Internal energy
• b) Heat
• c) Work
• d) All of these

Answer: Internal energy

Question: The internal energy of an ideal gas depends upon

• a) temperature
• b) specific volume
• c) pressure
• d) density

Answer: temperature

Question: Energy transfer brought about by moving the piston of a cylinder containing the gas is known as

• a) work
• b) heat
• c) pressure
• d) temperature

Answer: work

Question: The state of a thermodynamic system is represented by

• a) pressure, volume and temperature
• b) volume only
• c) pressure only
• d) number of moles

Answer: pressure, volume and temperature

Question: Which of the following parameters does not characterize the thermodynamic state of matter?

• a) Work
• b) Temperature
• c) Pressure
• d) Volume

Answer: Work

Question: At a given temperature the internal energy of a substance

• a) in liquid state is less than that in gaseous state.
• b) in liquid state is more than that in gaseous state
• c) is equal for the three states of matter.
• d) in liquid state is equal to that in gaseous state

Answer: in liquid state is less than that in gaseous state.

Question: The variable defined by Zeroth law of thermodynamics is

• a) temperature
• b) internal energy
• c) work
• d) All of these

Answer: temperature

Question: The first operation involved in a Carnot cycle is

• a) isothermal expansion
• b) adiabatic expansion
• c) isothermal compression
• d) adiabatic compression

Answer: isothermal expansion

Question: “Heat cannot by itself flow from a body at lower temperature to a body at higher temperature” is a statement or consequence of

• a) second law of thermodynamics
• b) conservation of momentum
• c) conservation of mass
• d) first law of thermodynamics

Answer: second law of thermodynamics

Question: Air conditioner is based on the principle of

• a) refrigerator
• b) first law of thermodynamics
• c) None of these
• d) Carnot cycle

Answer: refrigerator

Question: Which of the following processes is reversible?

• a) Isothermal compression
• b) Electrical heating of a nichrome wire
• c) Transfer of heat by radiation
• d) Transfer of heat by conduction

Answer: Isothermal compression

Question: Which of the following processes is irreversible?

• a) Transfer of heat by radiation
• b) Adiabatic changes performed slowly
• c) Extremely slow extension of a spring
• d) Isothermal changes performed slowly

Answer: Transfer of heat by radiation

Question: Heat engine is a device by which a system is made to undergo a ...X... process that result in conversion of ...Y... into work. Here, X and Y refer to

• a) cyclic and heat
• b) None of these
• c) isothermal and heat
• d) cyclic and work

Answer: cyclic and heat

Question: Which of the following statements is incorrect?

• a) All reversible cycles have same efficiency
• b) Reversible cycle has more efficiency than an irreversible one
• c) Carnot cycle is a reversible one
• d) Carnot cycle has the maximum efficiency in all cycles

Answer: All reversible cycles have same efficiency

Question: A refrigerator is a

• a) heat engine working in backward direction
• b) air cooler
• c) an electric motor
• d) heat engine

Answer: heat engine working in backward direction

Question: The temperature of source and sink of a heat engine are 127ºC and 27ºC respectively. An inventor claims its efficiency to be 26%, then:

• a) it is impossible
• b) it is possible with high probability
• c) it is possible with low probability
• d) data are insufficient

Answer: it is impossible

Question: If the co-efficient of performance of a refrigerator is 5 and operates at the room temperature 27°C, the temperature inside the refrigerator is

• a) 250 K
• b) 230 K
• c) 260 K
• d) 240 K

Answer: 250 K

Question. A thermodynamic system is taken through the cycle PQRSP process. The net work done by the system is:
a. 20 J
b. – 20 J
c. 400 J
d. – 374 J
Answer : B

Question. An ideal gas is taken around ABCA as shown in the above P-V diagram. The work done during a cycle is:

a. 2PV
b. PV
c. (1/2) PV
d. Zero
Answer : A

Question. If the ratio of specific heat of a gas at constant pressure to that at constant volume is γ , the change in internal energy of a mass of gas, when the volume changes from V to 2V constant pressure p, is:
a. R/(y - 1)
b. pV
c. pV/(y - 1)
d. ypV/(y - 1)
Answer : C

Question. A perfect gas goes from state A to another state B by absorbing 8 × 10⁵ J of heat and doing 6.5 × 10⁵ J of external work. It is now transferred between the same two states in another process in which it absorbs 10⁵ J of heat.
Then in the second process:
a. Work done on the gas is 0.5×10⁵ J
b. Work done by gas is 0.5×10⁵ J
c. Work done on gas is 10⁵ J
d. Work done by gas is 10⁵ J
Answer : A

Question. The relation between the internal energy U and adiabatic constant γ is:
a. U = PV/γ-1
b. U = PV1/γ -1
c. U = PV/γ
d. U = y/PV
Answer : A

Question. Water falls from a height of 210 m. assuming whole of energy due to fall is converted into heat the rise in temperature of water would be: (J = 4.3 Joule/cal)
a. 42°C
b. 49°C
c. 0.49°C
d. 4.9°C
Answer : C

Question. Hailstone at 0°C falls from a height of 1 km on an insulating surface converting whole of its kinetic energy into heat. What part of it will melt? (g =10m/ s² )
a. 1/33
b. 1/8
c. 1/33 x 10^-4
d. All of it will melt
Answer : A

Question. A gas is compressed at a constant pressure of 2 50N /m from a volume of 3 10m to a volume of 3 4m . Energy of 100 J is then added to the gas by heating. Its internal energy is:
a. Increased by 400 J
b. Increased by 200 J
c. Increased by 100 J
d. Decreased by 200 J
Answer : A

Question. A thermodynamic process is shown in the figure.

The pressures and volumes corresponding to some points in the figure are: P_A = 3 x 10⁴  P_a, P_B = 8 x 10⁴ P_a and V_A = 2x10^-3 m³. V_p = 5x10^-3 m³. In process AB, 600 J of heat is added to the system and in process BC, 200 J of heat is added to the system. The change in internal energy of the system in process AC would be:
a. 560 J
b. 800 J
c. 600 J
d. 640 J
Answer : A

Question. Work done per mol in an isothermal change is:
a. RTlog₁₀ V₂/V₁
b. RTlog₁₀ V₁/V₂
c. RTlog_e V₂/V₁
d. RTlog_e V₁/V₂
Answer : C

Question. Which of the following graphs correctly represents the variation of β = −(dV / dP) /V with P for an ideal gas at constant temperature?

Answer : A

Question. How much energy is absorbed by 10 kg molecule of an ideal gas if it expands from an initial pressure of 8 atm to 4 atm at a constant temperature of 27°C?
a. 1.728 ×10⁷J
b. 17.28 × 10⁷ J
c. 1.728 ×10⁹ J
d. 17.28 ×10⁹ J
Answer : A

Question. 5 Moles of an ideal gas undergoes an isothermal process at 500K in which its volume is doubled. The work done by the gas system is:
a. 3500 J
b. 14400 J
c. 17800 J
d. 5200 J
Answer : B

Question. During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its absolute temperature.
The ratio C_p / C_v for the gas is:
a. 2/3
b. 3/4
c. 2
d. 3/5
Answer : A

Question. An ideal gas at 27°C is compressed adiabatically to 8/27 of its original volume. If y = 5/3, then the rise in temperature is:
a. 450 K
b. 375 K
c. 225 K
d. 405 K
Answer : B

Question. P-V plots for two gases during adiabatic process are shown in the figure.

Plots 1 and 2 should correspond respectively to:
a. He and O₂
b. O₂ and He
c. He and Ar
d. O₂ and N₂
Answer : B

Question. A monoatomic ideal gas, initially at temperature T₁ , is enclosed in a cylinder fitted with a frictionless piston. The gas is allowed to expand adiabatically to a temperature T₂ by releasing the piston suddenly. If L₁ and L₂ are the lengths of the gas column before and after expansion respectively, then T₁ / T₂ is given by:
a. (L₁/L₂)^{2 / 3}
b. L₁/L₂
c. L₂/L₁
d. (L₂/L₁)^{2 / 3}
Answer : D

Question. Four curves A, B, C and D are drawn in the adjoining figure for a given amount of gas. The curves which represent adiabatic and isothermal changes are:

a. C and D respectively
b. D and C respectively
c. A and B respectively
d. B and A respectively
Answer : C

Question. 1 cm³ of water at its boiling point absorbs 540 calories of heat to become steam with a volume of 1671 cm³. If the atmospheric pressure is 1.013 × 10⁵ N/m² and the mechanical equivalent of heat = 4.19 J/calorie, the energy spent in this process in overcoming intermolecular forces is:
a. 540 calorie
b. 40 calorie
c. 500 calorie
d. Zero
Answer : C

Question. A thermally insulated container is divided into two parts by a screen. In one part the pressure and temperature are P and T for an ideal gas filled. In the second part it is vacuum. If now a small hole is created in the screen, then the temperature of the gas will:
a. Decrease
b. Increase
c. Remain same
d. None of these
Answer : C

Question. A gas expands 0.25 m3 at constant pressure 10³ N /m², the work done is:
a. 2.5 ergs
b. 250 J
c. 250 W
d. 250 N
Answer : B

Question. At 100°C the volume of 1kg of water is 10^–3 m³ and volume of 1 kg of steam at normal pressure is 1.671 m³. The latent heat of steam is 2.3×10⁶ J / kg and the normal pressure is 10⁵ N /m² . If 5 kg of water at 100°C is converted into steam, the increase in the internal energy of water in this process will be:
a. 8.35 ×10⁵ J
b. 10.66 ×10⁶ J
c. 11.5 ×10⁶ J
d. Zero
Answer : B

Question. In pressure-volume diagram given below, the isochoric, isothermal, and isobaric parts respectively, are:

a. BA, AD, DC
b. DC, CB, BA
c. AB, BC, CD
d. CD, DA, AB
Answer : D

Question. Molar specific heat of oxygen at constant pressure C_p = 7.2 cal / mol / °C and R = 8.3 J/mol/K. At constant volume, 5 mol of oxygen is heated from 10°C to 20°C, the quantity of heat required is approximately:
a. 25 cal
b. 50 cal
c. 250 cal
d. 500 cal
Answer : C

Question. The P-V diagram of a system undergoing thermodynamic transformation is shown in figure. The work done on the system in going from A → B → C is 50 J and 20 cal heat is given to the system. The change in internal energy between A and C is:

a. 34 J
b. 70 J
c. 84 J
d. 134 J
Answer : D

Question. A bullet moving with a uniform velocity v, stops suddenly after hitting the target and the whole mass melts be m, specific heat S, initial temperature 25°C, melting point 475°C and the latent heat L. Then:
a. mL = ms (475 - 25) + mv²/2J
b. ms (475 - 25) + mL = mv²/2J
c. ms (475 - 25) + mL = mv²/2J
d. ms (475 - 25) - mL = mv²/2J
Answer : B

Question. A lead bullet at 27°C just melts when stopped by an obstacle. Assuming that 25% of heat is absorbed by the obstacle, then the velocity of the bullet at the time of striking: (M.P. of lead = 327°C, specific heat of lead = 0.03 cal/gm °C, latent heat of fusion of lead = 6 cal/gm and J = 4.2 J/cal)
a. 410 m/sec
b. 1230 m/sec
c. 307.5 m/sec
d. None of these
Answer : A

Question. If 150 J of heat is added to a system and the work done by the system is 110 J, then change in internal energy will be:
a. 260 J
b. 150 J
c. 110 J
d. 40 J
Answer : D

Question. If ΔQ and ΔW represent the heat supplied to the system and the work done on the system respectively, then the first law of thermodynamics can be written as:
a. ΔQ = ΔU + ΔW
b. ΔQ = ΔU − ΔW
c. ΔQ = ΔW − ΔU
d. ΔQ = −ΔW − ΔU
Answer : B

Question. When an ideal diatomic gas is heated at constant pressure, the fraction of the heat energy supplied which increases the internal energy of the gas is:
a. 2/5
b. 3/5
c. 3/7 
d. 5/7
Answer : D

Question. An electric fan is switched on in a closed room. The air in the room is:
a. Cooled
b. Heated
c. Maintains its temperature
d. Heated or cooled depending on the atmospheric Pressure
Answer : B

Question. An ideal gas is taken through the cycle A → B → C → A, as shown in the figure

If the net heat supplied to the gas in the cycle is 5 J, the work done by the gas in the process C → A is:
a. – 5 J
b. – 20 J
c. – 15 J
d.– 10 J
Answer : A

Question. If the door of a refrigerator is kept open, then which of the following is true?
a. Room is cooled
b. Room is heated
c. Room is either cooled or heated
d. Room is neither cooled nor heated
Answer : B

Question. A Carnot engine working between 300 K and 600K has work output of 800 J per cycle. What is amount of heat energy supplied to the engine from source per cycle?
a. 1800 J/cycle
b. 1000 J/cycle
c. 2000 J/cycle
d. 1600 J/cycle
Answer : D