JEE Physics Thermodynamics MCQs Set C

Question:

• a) 1000 J
• b) Zero
• c) –2000 J
• d) 2000 J

Answer: 1000 J

Question:

• a)

  

• b)

  

• c) Cannot be predicted
• d) None of these

Answer:

Question: One mole of an ideal gas goes from an initial state A to final state B via two processes: It first undergoes isothermal expansion from volume V to 3V and then its volume is reduced from 3V to V at constant pressure. The correct P-V diagram representing the two processes is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 6 J
• b) 10 J
• c) 12 J
• d) 36 J

Answer:  6 J

Question:

• a) 2 PV
• b) 4 PV
• c) PV
• d)

  

Answer:  2 PV

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: 150 J of heat has been removed from the gas

Question:

• a)

  

• b)

  

• c)

  

• d) 2

Answer:

Question:

• a) 256 atm
• b) 8 atm
• c) 28 atm
• d) 68.7 atm

Answer: 256 atm

Question:

• a) 5.46 J/K
• b) 7.46 J/K
• c) 3.46 J/K
• d) 1.46 J/K

Answer: 5.46 J/K

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: –33°C

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:  E = 0

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: 1164 K

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: 600 K

Question: An ideal gas, undergoing adiabatic change, has which of the following pressure temperature relationship?

• a)

  

• b)

  

• c)

  

• d) None of these

Answer:

Question:

• a) Isobaric
• b) Isothermal
• c) Equal in all cases
• d) Adiabatic

Answer: Isobaric

Question: The efficiency of a Carnot engine operating with reservoir temperature of 100°C and – 23°C will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d) PV

Answer:

Question:

• a) 375 K
• b) 475 K
• c) 175 K
• d) 275 K

Answer: 375 K

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: 37°C, 99°C

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: It is impossible

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: 400 K

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: 1.2

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: (T – 4) K

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: Isothermal compression

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: 250 K

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: 99°C

Question: In thermodynamic processes which of the following statements is not true?

• a) In an isochoric process pressure remains constant
• b) In an adiabatic process the system is insulated from the surroundings
• c) In an isothermal process the temperature remains constant
• d)

  

Answer: In an isochoric process pressure remains constant

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: 7900 J

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Which of the following relations does not give the equation of an adiabatic process, where terms have their usual meaning?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: R^–6

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: 2P

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^–2

Question:

• a) 32 P₁
• b) 16 P₁
• c) P₁
• d) 64 P₁

Answer: 32 P₁

Question:  At 10^oC the value of the density of a fixed mass of an ideal gas divided by its pressure is x. At 110^oC this ratio is

• a)

  

• b)

  

• c)

  

• d) x

Answer:

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: Kinetic energy

Question: The value of critical temperature in terms of van der Waals’ constants a and b is given by

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The degrees of freedom of a triatomic gas is (Consider moderate temperature)

• a) 6
• b) 4
• c) 2
• d) 8

Answer: 6