NEET Physics Carnot Engine Refrigerator and Second Law of Thermodynamics MCQs Set A

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: A

Question. Air conditioner is based on the principle of
(a) refrigerator
(b) Carnot cycle
(c) first law of thermodynamics
(d) None of these

Answer: A

Question. Which of the following processes is reversible?
(a) Isothermal compression
(b) Transfer of heat by radiation
(c) Transfer of heat by conduction
(d) None of these

Answer: A

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: A

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 t o
(a) cyclic and heat
(b) adiabatic and heat
(c) isothermal and heat
(d) cyclic and work

Answer: A

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: A

Question. A refrigerator is a
(a) heat engine working in backward direction
(b)   air cooler
(c) an electric motor
(d) heat engine

Answer: A

Question. A Carnot engine works between a source and a sink maintained at constant temperatures T1 and T2. For efficiency to be the greatest
(a) T₁ and T₂ should be low
(b) T₁ and T₂ should be high
(c) Both
(d) None of these

Answer: A

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: A

Question. A steam engine takes 0.1 kg of steam at 100°C per minute and cools it down to 20°C. What is the heat rejected by the steam engine per second? [Latent heat of vaporization of steam = 540 cal g^–1]
(a) 1.03 × 10³ cal/sec
(b) 62 × 10³ cal/sec
(c) 6.2 × 10⁴ cal/sec
(d) None of these

Answer: A

Question. Even Carnot engine cannot give 100% efficiency because we cannot
(a) reach absolute zero temperature
(b) eliminate friction
(c) find ideal sources
(d) prevent radiation

Answer: A

Question. In all natural processes, the entropy of the universe
(a) always increases
(b) may increase or decrease
(c) always decreases
(d) remains constant

Answer: A

Question. If an air conditioner is put in the middle of a room and started working
(a) the room will become slightly warmer
(b) the same temperature will be attained in the room as by putting it on the window in the standard position
(c) the temperature of the room will not change
(d) the room can be cooled slightly

Answer: A

Question. Two bodies each of mass M and temperature independent specific heat C are initially at temperatures 100 K and 400 K. A reversible engine is used to extract heat with the hotter body as the source and cooler body as the sink. Both the bodies attain the same final temperature. Then,
(a) total change in entropy of the system is zero.
(b) the total heat extracted from the hotter body is 150 MC
(c) the work done by the engine is 500 MC
(d) the final temperature of the two bodies is 250K.

Answer: A

Question. A body of mass m with specific heat C at temperature 500 K is brought into contact with an identical body at temperature 100 K. The system is isolated from the surroundings during the process. The change in entropy of the system is
(a) mC ln (9/5)
(b) mC ln (5/3)
(c) mC ln 5
(d) mC ln 3

Answer: A

Question. A Carnot engine whose low temperature reservoir is at 7°C has an efficiency of 50%. It is desired to increase the efficiency to 70%. By how many degrees should the temperature of the high temperature reservoir be increased?
(a) 380 K
(b) 560 K
(c) 280 K
(d) 840 K

Answer: A

Question. In a Carnot engine, the temperature of reservoir is 927°C and that of sink is 27°C. If the work done by the engine when it transfers heat from reservoir to sink is 12.6 × 10⁶J, the quantity of heat absorbed by the engine from the reservoir is
(a) 16.8 × 10⁶ J
(b) 7.6 × 10⁶ J
(c) 4 × 10⁶ J
(d) 4.2 × 10⁶ J

Answer: A

Question. A Carnot engine absorbs 1000 J of heat energy from a reservoir at 127°C and rejects 600 J of heat energy during each cycle. The efficiency of engine and temperature of sink will be:
(a) 40% and – 33°C
(b) 70% and – 10°C
(c) 20% and – 43°C
(d) 50% and – 20°C

Answer: A

Question. Assertion : The efficiency of a reversible engine is maximum.
Reason : In such a device no dissipation of energy takes place.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct

Answer: A

Question. When 1 kg of ice at 0°C melts to water at 0°C, the resulting change in its entropy, taking latent heat of ice to be 80 cal/°C, is
(a) 293 cal/K
(b) 253 cal/K
(c) 273 cal/K
(d) None of these

Answer: A

Question. A Carnot engine is working between 127°C and 27°C. The increase in efficiency will be maximum when the temperature of
(a) the sink is decreased by 50°C
(b) source is increased by 25°C and that of sink is decreased by 25°C
(c) both source and sink are decreased by 25°C each.
(d) the source is increased by 50°C

Answer: A

Question. Assertion : When a glass of hot milk is placed in a room and allowed to cool, its entropy decreases
Reason : Allowing hot object to cool does not violate the second law of thermodynamics.
(a) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(b) Assertion is correct, reason is incorrect
(c) Assertion is incorrect, reason is correct
(d) Assertion is correct, reason is correct; reason is a correct explanation for assertion

Answer: A

Question. A Carnot engine whose efficiency is 50% has an exhaust temperature of 500 K. If the efficiency is to be 60% with the same intake temperature, the exhaust temperature must be (in K)
(a) 400
(b) 600
(c) 200
(d) 800

Answer: A

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: A

Question. A diatomic ideal gas is used in a car engine as the working substance. If during the adiabatic expansion part of the cycle, volume of the gas increases from V to 32 V, the efficiency of the engine is
(a) 0.75
(b) 0.99
(c) 0.25
(d) None of the options

Answer: A

Question. A Carnot engine takes 3 × 10⁶ cal. of heat from a reservoir at 627°C, and gives it to a sink at 27°C. The work done by the engine is
(a) 8.4 × 10⁶ J
(b) 4.2 × 10⁶ J
(c) 16.8 × 10⁶ J
(d) zero

Answer: A