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: A

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: A

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: A

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: A

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: A

Question. Which of the following can be coefficient of performance of refrigerator?
(a) All of these
(b) 9
(c) 0.5
(d) 1

Answer: A

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: A

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: 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 to as to increase its efficiency by 50% of original efficiency?
(a) 250 K
(b) 300 K
(c) 450 K
(d) 150 K

Answer: A

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: A

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: A

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: A

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: A

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: A

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: A

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: A

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: A

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: 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) 273 cal/K
(c) 8 × 10⁴ cal/K
(d) 80 cal/K

Answer: A

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: A

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: A