# IC Engine Questions and Answers – Carnot Cycle

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This set of IC Engines Multiple Choice Questions & Answers (MCQs) focuses on “Carnot Cycle”.

1. In a carnot cycle, the working medium receives heat at a _____________ temperature.
a) lower
b) higher
c) constant
d) none of the mentioned

Explanation: In a carnot cycle the working medium receives heat at a higher temperature and rejects heat at a lower temperature.

2. In a carnot cycle, the working medium rejects heat at a ____________ temperature.
a) lower
b) higher
c) constant
d) none of the mentioned

Explanation: In a carnot cycle the working medium receives heat at a higher temperature and rejects heat at a lower temperature.

3. In a carnot cycle, what is the working fluid?
a) a real gas
b) an ideal gas
c) a natural gas
d) none of the mentioned

Explanation: As Carnot cycle is an ideal cycle, so the working fluid is an ideal gas.
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4. The isothermal process of a carnot cycle needs very __________ motion of the piston to maintain constant temperature.
a) slow
b) fast
c) medium
d) none of the mentioned

Explanation: The isothermal process of a carnot cycle needs very slow motion of the piston to maintain constant temperature while the adiabatic process needs very fast motion to complete the adiabatic process.

5. The adiabatic process of a carnot cycle needs very __________ motion to complete the adiabatic process.
a) slow
b) fast
c) medium
d) none of the mentioned

Explanation: The isothermal process of a carnot cycle needs very slow motion of the piston to maintain constant temperature while the adiabatic process needs very fast motion to complete the adiabatic process.

6. For a given temperature T1, as the difference between T1 and T2 increases, the COP of a carnot heat pump ___________
a) increases
b) decreases
c) first increases, then decreases
d) none of the mentioned

Explanation: COP(heat pump) = T1/(T1 – T2)
As the value of T1 – T2 increases, value of COP decreases.

7. A carnot heat pump is used to heat a house. The outside temperature is -3ºC and the indoor temperature is 27ºC. If the heat loss from the house is 40kW, the power required to operate the heat pump is?
a) 1kW
b) 2kW
c) 3kW
d) 4kW

Explanation: COP(heat pump) = Heat loss/Work done = T1/(T1 – T2)
or, 40/ Work done = 273 + 27/27-(-3)
or, Work done = 40 x 30/300 = 4kW.

8. A carnot cycle is to be designed to attain efficiency of 0.75. if temperature of high temperature reservoir is 727ºC, then low temperature reservoir will have to be maintained at ___________
a) 23ºC
b) 181ºC
c) -23ºC
d) -181ºC

Explanation: Carnot efficiency = T2– T1/(T2+273)
or, 0.75 = 727- T1/(727+273)
or, 0.75×1000 = 727- T1
or, – T1 = 750-727
or, T1 = -23ºC.

9. A cyclic heat engine does 50kJ of work per cycle. If efficiency of engine is 75%, the heat rejected per cycle will be ___________
a) 60.6kJ
b) 16.6kJ
c) 66.6kJ
d) 200kJ

Explanation: Carnot efficiency = Work done/Heat supplied(Q1)
0.75 = 50/ Q1
or, Q1 = 200/3
and, Work done = Q1– Q2
or, Q2 = 200/3-50 = 50/3 = 16.6kJ.

10. A carnot cycle refrigerator operates between 250ºK and 300ºK. What is the value of COP?
a) 10
b) 20
c) 25
d) 5

Explanation: COP = T2/(T1 – T2)
= 250/300-250
= 5.

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