JEE Physics Thermodynamics MCQs Set B

Question: In a Carnot engine, when heat is absorbed from the source, temperature of source

• a) Remains constant
• b) Increases
• c) Decreases
• d) Cannot say

Answer: Remains constant

Question: Carnot engine working between 300 K and 600 K has a work output of 800 J per cycle. The amount of heat energy supplied to engine from the source in each cycle is

• a) 1600 J
• b) 800 J
• c) 3200 J
• d) 6400 J

Answer: 1600 J

Question: An ideal heat engine operates on Carnot cycle between 227°C and 127°C. It absorbs 6 × 10⁴ cal at the higher temperature. The amount of heat converted into work equals to

• a) 1.2 × 10⁴ cal
• b) 1.6 × 10⁴ cal
• c) 3.5 × 10⁴ cal
• d) 4.8 × 10⁴ cal

Answer: 1.2 × 10⁴ cal

Question: The maximum possible efficiency of a heat engine is

• a)

  

• b)

  

• c)

  

• d) 100%

Answer:

Question: A frictionless heat engine can be 100% efficient only if its exhaust temperature is

• a) 0 K
• b) Equal to its input temperature
• c) Less than its input temperature
• d) 0°C

Answer: 0 K

Question: A reversible engine and an irreversible engine are working between the same temperatures. The efficiency of the

• a) Reversible engine is greater
• b) Two engines cannot be compared
• c) Two engines are same
• d) Irreversible engine is greater

Answer: Reversible engine is greater

Question: Which of the following can be coefficient of performance of refrigerator?

• a) All of these
• b) 9
• c) 0.5
• d) 1

Answer: All of these

Question: The temperature inside and outside a refrigerator are 273 K and 300 K respectively. Assuming that the refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surrounding will be nearly

• a) 11 J
• b) 22 J
• c) 33 J
• d) 50 J

Answer: 11 J

Question: By opening the door of a refrigerator placed inside a room you

• a) Ultimately warm the room slightly
• b) Can neither cool nor warm the room
• c) Can cool it to the temperature inside the refrigerator
• d) Can cool the room to certain degree

Answer: Ultimately warm the room slightly

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 to as to increase its efficiency by 50% of original efficiency?

• a) 250 K
• b) 300 K
• c) 450 K
• d) 150 K

Answer: 250 K

Question: A container is filled with 20 moles of an ideal diatomic gas at absolute temperature T. When heat is supplied to gas temperature remains constant but 8 moles dissociate into atoms. Heat energy given to gas is

• a) 4RT
• b) 6RT
• c) 3RT
• d) 5RT

Answer: 4RT

Question: Liquid oxygen at 50 K is heated to 300 K at constant pressure of 1 atm. The rate of heating is constant. Which one of the following graphs represents the variation of temperature with time?

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: 3 moles of an ideal gas are contained within a cylinder by a frictionless piston and are initially at temperature T. The pressure of the gas remains constant while it is heated and its volume doubles. If R is molar gas constant, the work done by the gas in increasing its volume is

• a)

  3RT

• b)

  

• c)

  

• d)  3RT ln 2

Answer: 3RT

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A triatomic, diatomic and monatomic gas is supplied same amount of heat at constant pressure, then

• a) Fractional energy used to change internal energy is maximum in triatomic gases
• b) Fractional energy used to change internal energy is maximum in diatomic gas
• c) Fractional energy used to change internal energy is maximum in monatomic gas
• d) Fractional energy used to change internal energy is same in all the three gases

Answer: Fractional energy used to change internal energy is maximum in triatomic gases

Question:

• a) 75 cal
• b) 70 cal
• c) 90 cal
• d) 50 cal

Answer: 75 cal

Question:  To an ideal triatomic gas 800 cal heat energy is given at constant pressure. If vibrational mode is neglected, then energy used by gas in work done against surroundings is

• a) 200 cal
• b) 300 cal
• c) 400 cal
• d) 60 cal

Answer: 200 cal

Question:  A closed cylindrical vessel contains N moles of an ideal diatomic gas at a temperature T. On supplying heat, temperature remains same, but n moles get dissociated into atoms. The heat supplied is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

More Questions..............................

Question: An ideal monatomic gas at 300 K expands adiabatically to 8 times its volume. What is the final temperature?

• a) 75 K
• b) 300 K
• c) 560 K
• d) 340 K

Answer: 75 K

Question:

• a) 5 × 10⁵ N/m²
• b) 6 × 10⁵ N/m²
• c) 10 × 10⁵ N/m²
• d) 3 × 10⁵ N/m²

Answer: 5 × 10⁵ N/m²

Question: A gas may expand either adiabatically or isothermally. A number of P–V curves are drawn for the two processes over different range of pressure and volume. It will be found that

• a) All of these
• b) Two isothermal curves do not intersect
• c) Two adiabatic curves do not intersect
• d) An adiabatic curve and an isothermal curve may intersect

Answer: All of these

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) Monatomic
• b) Polyatomic
• c) Diatomic
• d) Mixture of monatomic and diatomic

Answer: Monatomic

Question:

• a) Net heat energy has been supplied to the system
• b) Temperature of the gas is maximum at state B
• c) In process CA, heat energy is absorbed by system
• d) Work done by gas in process AB is more than that in the process BC

Answer: Net heat energy has been supplied to the system

Question: A diatomic gas undergoes a process represented by PV^1.3 = constant. Choose the incorrect statement

• a) None of these
• b) The work done by surroundings during expansion of the gas is negative
• c) The gas cools down during expansion
• d) The gas expands by absorbing heat from the surroundings

Answer: None of these

Question:

• a) 9 J
• b) 11 J
• c) 12 J
• d) 8 J

Answer: 9 J

Question:

• a) Temperature first increases and then decreases
• b) Temperature increases continuously
• c) Temperature first decreases and then increases
• d) Temperature decreases continuously

Answer: Temperature first increases and then decreases

Question:

• a) During process BC internal energy of system increases
• b) During process BC internal energy of the system decreases
• c) During process AB, work done by the gas is positive
• d) During process CD, work done by gas is negative

Answer: During process BC internal energy of system increases

Question: A hydrogen cylinder is designed to withstand an internal pressure of 100 atm. At 27°C, hydrogen is pumped into the cylinder which exerts a pressure of 20 atm. At what temperature does the danger of explosion first sets in?

• a) 1500 K
• b) 500 K
• c) 1000 K
• d) 2000 K

Answer: 1500 K

Question:

• a) 4P
• b) 6P
• c) 3P
• d) P

Answer:  4P

Question:

• a) 2.5 R
• b) 4.2 R
• c) 3.25 R
• d) 1.7 R

Answer: 2.5 R

Question:  An ideal gas expands according to the law P2V = constant. The internal energy of the gas

• a) Increases continuously
• b) Remain constant
• c) Decreases continuously
• d) First increases and then decreases

Answer: Increases continuously

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Neon gas of a given mass expands isothermally to double volume. What should be the further fractional decrease in pressure, so that the gas when adiabatically compressed from that state, reaches the original state?

• a) 1 – 2^–2/3
• b) 1 – 3^1/3
• c) 2^1/3
• d) 3^2/3

Answer: 1 – 2^–2/3

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) 273 cal/K
• c) 8 × 10⁴ cal/K
• d) 80 cal/K

Answer:  293 cal/K

Question:

• a) AB
• b) BC
• c) CD
• d) DA

Answer: AB

Question: Efficiency of a heat engine working between a given source and sink is 0.5. Coefficient of performance of the refrigerator working between the same source and the sink will be

• a) 1 
• b) 0.5
• c) 1.5
• d) 2

Answer: 1

Question: A heat engine rejects 600 cal to the sink at 27°C. Amount of work done by the engine will be (Temperature of source is 227°C & J = 4.2 J/cal)

• a) 1680 J
• b) 840 J
• c) 2520 J
• d) None of these

Answer:  1680 J