Solved Practice Questions on Carnot Engine | Physical Chemistry PDF Download

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

Correct Answer is option (b)
In a carnot cycle the working medium receives heat at a higher temperature and rejects heat at a lower temperature.

Q.2. 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

Correct Answer is option (b)
As Carnot cycle is an ideal cycle, so the working fluid is an ideal gas.

Q.3. 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

Correct Answer is option (b)
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.

Q.4. 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

Correct Answer is option (d)
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.

Q.5. 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

Correct Answer is option (b)
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.

Q.6. In a carnot cycle, the working medium rejects heat at a ____________ temperature.
(a) lower
(b) higher
(c) constant
(d) none of the mentioned

Correct Answer is option (a)
In a carnot cycle the working medium receives heat at a higher temperature and rejects heat at a lower temperature.

Q.7. 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

Correct Answer is option (a)
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.

Q.8. 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

Correct Answer is option (b)
COP(heat pump) = T₁/(T₁ – T₂)
As the value of T₁ – T₂ increases, value of COP decreases.

Q.9. 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

Correct Answer is option (c)
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.

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

Correct Answer is option (d)
COP = T₂/(T₁ – T₂)
= 250/300-250
= 5.