BITSAT Physics Thermodynamics MCQs

Question: A cyclic process ABCD is shown in the figure PV diagram. Which of the following curves represent the same process?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: One mole of an ideal gas is taken from state A to state B by three different processes, (i) ACB (ii) ADB (iii) AEB as shown in the P-V diagram. The heat absorbed by the gas is

• a) Greater in process (ii) than in (i)
• b) The least in process (ii)
• c) The same in (i) and (iii)
• d) Less in (iii) than in (ii)

Answer: Less in (iii) than in (ii)

Question:  Figure below shows two paths that may be taken by a gas to go from a state A to a state (c)

 In process AB, 400 J of heat is added to the system and in process BC, 100 J of heat is added to the system. The heat absorbed by the system in the process AC will be

• a) 500 J
• b) 460 J
• c) 300 J
• d) 380 J

Answer: 460 J

Question:  0.5 mole of an ideal gas at constant temperature 27°C kept inside a cylinder of length L and crosssection area A closed by a massless piston.  The cylinder is attached with a conducting rod of length L, cross-section area (1/9) m² and thermal conductivity k, whose other end is maintained at 0°C. If piston is moved such that rate of heat flow through the conducing rod is constant then velocity of piston when it is at height L/2 from the bottom of cylinder is : [Neglect any kind of heat loss from system]

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: One mole of O₂ gas having a volume equal to 22.4 Litres at 0°C and 1 atmospheric pressure in compressed isothermally so that its volume reduces to 11.2 litres. The work done in this process is-

• a) 1672.5 J
• b) 1728 J
• c) –1728 J
• d) –1572.5 J

Answer: –1572.5 J

Question: A Carnot’s heat engine works between the temperatures 427°C and 27°C. What amount of heat should it consume per second to deliver mechanical work at the rate of 1.0 kW ?

• a) 0.417 kcal/s
• b) 4.17 kcal/s
• c) 41.7 kcal/s
• d) 0.212 kcal/s

Answer: 0.417 kcal/s

Question: Which of the following process is possible according to the first law of thermodynamics –

• a) W > 0, Q < 0 and dU = 0
• b) W > 0, Q < 0 and dU > 0
• c) W > 0, Q < 0 and dU < 0
• d) W < 0, Q > 0 and dU < 0

Answer: W > 0, Q < 0 and dU < 0

Question: For an isothermal expansion of a perfect gas, the value of  is equal to

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Figure shows the variation of internal energy (U) with the pressure (P) of 2.0 mole gas in cyclic process abcda. The temperature of gas at c and d are 300 K and 500 K. Calculate the heat absorbed by the gas during the process.

• a) 400 R ln 2
• b) 200 R ln 2
• c) 100 R ln 2
• d) 300 R ln 2

Answer: 400 R ln 2

Question: In the equation PVg = constant, the value of γ is unity. Then the process is

• a) Isothermal
• b) Adiabatic
• c) Isobaric
• d) Irreversible

Answer: Isothermal

Question: An ideal refrigerator has a freezer at a temperature of 13ºC. The coefficient of performance of the engine is 5. The temperature of the air (to which heat is rejected) is

• a) 320ºC
• b) 39ºC
• c) 325 K
• d) 325ºC

Answer: 39ºC

Question: A sample of gas expands from volume V₁ to V₂. The amount of work done by the gas is greatest when the expansion is

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

Answer: Isothermal

Question: A cyclic process is shown in the p-T diagram. Which of the curves show the same process on a P-V diagram ?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: The slopes of isothermal and adiabatic curves are related as

• a) Isothermal curve slope = adiabatic curve slope
• b) Isothermal curve slope = g × adiabatic curve slope
• c) Adiabatic curve slope = g × isothermal curve slope
• d) adiabatic curve slope sothermal curve slope

Answer: Adiabatic curve slope = g × isothermal curve slope

Question: A Carnot engine works first between 200°C and 0°C and then between 0°C and –200°C. The ratio of its efficiency in the two cases is

• a) 1.0
• b) 0.577
• c) 0.34
• d) 0.68

Answer: 1.0

Question: An ideal gas with adiabatic exponent (γ = 1.5) undergoes a process in which work done by the gas is same as increase in internal energy of the gas. The molar heat capacity of gas for the process is –

• a) C = 4R
• b) C = 0
• c) C = 2R
• d) C = R

Answer: C = 4R

Question: A cylinder with a movable piston contains 3 moles of hydrogen at standard temperature and pressure. The walls of the cylinder are made of a heat insulator, and the piston is insulated by having a pile of sand on it. By what factor does the pressure of the gas increases if the gas is compressed to half its original volume ?

• a) (2)^7/5
• b) (2)^1/5
• c) (5)^7/5
• d) (2)^1/5

Answer: (2)^7/5

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: Which of the following process is possible according to the first law of thermodynamics –

• a) W > 0, Q < 0 and dU = 0
• b) W > 0, Q < 0 and dU > 0
• c) W > 0, Q < 0 and dU < 0
• d) W < 0, Q > 0 and dU < 0

Answer: W > 0, Q < 0 and dU < 0

Question: A Carnot’s heat engine works between the temperatures 427°C and 27°C. What amount of heat should it consume per second to deliver mechanical work at the rate of 1.0 kW ?

• a) 0.417 kcal/s
• b) 4.17 kcal/s
• c) 41.7 kcal/s
• d) 0.212 kcal/s

Answer: 0.417 kcal/s