JEE Physics Thermodynamics MCQs Set C

Question. During an isothermal expansion, a confined ideal gas does –150 J of work against its surrounding. This implies that
(a) 150 J of heat has been removed from the gas
(b) 150 J of heat has been added to the gas
(c) 300 J of heat has been added to the gas
(d) No heat is transferred because the process is isothermal

Answer: A

Question. A Carnot engine has efficiency 25%. It operates between reservoirs of constant temperatures with temperature difference of 80°C. What is the temperature of the low-temperature reservoir?
(a) –33°C
(b) 33°C
(c) 25°C
(d) –25°C

Answer: B

Question. If Q, E and W denote respectively the heat added, change in internal energy and the work done in a closed cycle process, then
(a) E = 0
(b) Q = W = 0
(c) W = 0
(d) Q = 0

Answer: A

Question. A monatomic gas initially at 18°C is compressed adiabatically to one eighth of its original volume. The temperature after compression will be
(a) 1164 K
(b) 144 K
(c) 18 K
(d) 887.4 K

Answer: A

Question. An ideal Carnot engine, whose efficiency is 40%, receives heat at 500 K. If its efficiency is 50%, then the intake temperature for the same exhaust temperature is
(a) 600 K
(b) 700 K
(c) 900 K
(d) 800 K

Answer: A

Question. The (W/Q) of a Carnot engine is 1/6. Now the temperature of sink is reduced by 62°C, then this ratio becomes twice, therefore the initial temperature of the sink and source are respectively
(a) 37°C, 99°C
(b) 67°C, 33°C
(c) 97K, 37K
(d) 33°C, 67°C

Answer: A

Question. A scientist says that the efficiency of his heat engine which works at source temperature 127°C and sink temperature 27°C is 26%, then
(a) It is impossible
(b) It is quite probable
(c) It is possible but less probable
(d) Data are incomplete

Answer: A

Question. The efficiency of Carnot engine is 50% and temperature of sink is 500 K. If temperature of source is kept constant and its efficiency raised to 60%, then the required temperature of sink will be
(a) 400 K
(b) 500 K
(c) 600 K
(d) 100 K

Answer: A

Question. An ideal gas heat engine operates in a Carnot cycle between 227°C and 127°C. It absorbs 6 kcal at the higher temperature. The amount of heat (in kcal) converted into work is equal to
(a) 1.2
(b) 1.6
(c) 3.5
(d) 4.8

Answer: A

Question. One mole of an ideal gas at an initial temperature of T K does 6R joules of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is 5/3, the final temperature of gas will be
(a) (T – 4) K
(b) (T + 4) K
(c) (T – 2.4) K
(d) (T + 2.4) K

Answer: A

Question. Which of the following processes is reversible
(a) Isothermal compression
(b) Transfer of heat by conduction
(c) Transfer of heat by radiation
(d) Electrical heating of a nichrome wire

Answer: A

Question. A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency?
(a) 250 K
(b) 325 K
(c) 275 K
(d) 380 K

Answer: A

Question. An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62°C, its efficiency is doubled. Temperatures of the source is
(a) 99°C
(b) 124°C
(c) 62°C
(d) 37°C

Answer: A

Question. The internal energy change in a system that has absorbed 2 kcals of heat and done 500 J of work is
(a) 7900 J
(b) 8900 J
(c) 6400 J
(d) 5400 J

Answer: A

Question. According to C.E. van der Waal, the interatomic potential varies with the average interatomic distance (R) as
(a) R^–6
(b) R^–4
(c) R^–2
(d) R^–1

Answer: A

Question. In a vessel, the gas is at a pressure P. If the mass of all the molecules is halved and their speed is doubled, then the resultant pressure will be
(a) 2P
(b) P
(c) P/2
(d) 4P

Answer: B

Question. The mean free path of collision of gas molecules varies with its diameter (d) of the molecules as
(a) d^–2
(b) d^–3
(c) d^–4
(d) d^–1

Answer: D

Question. At 0 K, which of the following properties of a gas will be zero?
(a) Kinetic energy
(b) Potential energy
(c) Density
(d) Volume

Answer: A

Question. The degrees of freedom of a triatomic gas is (Consider moderate temperature)
(a) 6
(b) 4
(c) 2
(d) 8

Answer: A