Questions on Carnot Engine with Answers

Practice Questions on Carnot Engine with Answers

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Questions on Carnot Engine with Answers


Q1. As shown on the P-V diagram, AB and CD are two isotherms at temperatures T1 and T2 respectively (T1 > T2), AC and BD are two reversible adiabats. In this Carnot Cycle, which of the following statements are true ?

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(a) Q1/T1 = Q2/T2
(b) the entropy of the source decreases
(c) the entropy of the system increases
(d) work done by the system W = Q1 – Q2


Q2. Two reversible heat engines A and B are arranged is series, A rejecting heat directly to B. Engine A receives 200 KJ at a temperature of 421oC from a hot source, while engine B is in communication with a cold sink at a temperature of 4.4oC. If the work output of A is twice that of B. Then, which of the following is/are correct ?

(a) The intermediate temperature between A and B is 143.4oC.
(b) The efficiency of engine A and B are 40% and 33.5% respectively.
(c) The efficiency of engine A and B are 33.5% and 40% respectively.
(d) The heat rejected to the cold sink is 80 KJ


Q3. A reversible heat engine operates between two reservoirs at temperatures of 600oC and 40oC. The engine drives a reversible refrigerator which operates between reservoirs at temperatures of 40oC and -20oC. The heat transfer to the heat engine is 2000KJ and net-work output of the combined engine refrigerator plant is 360 KJ. What is the heat transfer to the refrigerant and the net heat transfer to the reservoir at 40oC ?

(a) The heat transfer to the refrigerant is 3899 KJ.
(b) The heat transfer to the refrigerant is 4899 KJ.
(c) The net heat transfer to the reservoir at 40oC is 5539 KJ.
(d) The net heat transfer to the reservoir at 40oC is 6539 KJ.


Q4. Efficiency of a perfectly reversible (Carnot) heat engine operating between absolute temperature T and zero is equals to

(a) 0
(b) 0.5
(c) 0.75
(d) 1


Q5. The efficiency of a Carnot Engine operating between the temperature Th and Tc , where Th > Tc , is given by

(a) 1+Tc/Th
(b) 1-Tc/Th
(c) Tc/Th
(d) Tc – Th


Q6. A Carnot engine works between ice temperature (0oC) and the steam temperature (100oC). Its efficiency is :

(a) 36.6 %
(b) 37.8 %
(c) 26.8 %
(d) 73.2 %


Q7. A Carnot engine operates between temperature T1 and T2 with T1 > T2 . If W is the work done by the engine in one cycle, then the heat Q1 absorbed at T1 and Q2 rejected at T2 are

(a) Q1 = T2W/T1+T2 , Q2 = T1W/T1+T2
(b) Q1 = T1W/T1+T2 , Q2 = T2W/T1+T2
(c) Q1 = T2W/T1-T2 , Q2 = T1W/T1-T2
(d) Q1 = T1W/T1-T2 , Q2 = T2W/T1-T2


Q8. A Carnot engine whose low temperature reservoir at 7oC has an efficiency of 50% . It is desired to increase the efficiency to 70%. By how many degrees should the temperature of the high temperature reservoir be increased ?

(a) 273.3 K
(b) 373.3 K
(c) 37.3 K
(d) 27.3 K


Q9. Which is the more effective way to increase the efficiency of a Carnot engine, if T1 and T2 are the temperatures of the source and the sink respectively ?

(a) Increase T1 keeping T2 constant
(b) Decrease T1 keeping T2 constant
(c) Increase T2 keeping T1 constant
(d) Decrease T2 keeping T1 constant


Q10. The efficiency of a Carnot engine cycle is 1/6 . On reducing the temperature of the sink by 65oC, the efficiency increases to 1/3 .The initial and the final temperature between which cycle is working is

(a) 117oC and 52oC
(b) 152oC and 217oC
(c) 217oC and 152oC
(d) 52oC and 117oC


Q11. A Carnot engine can be used to define an absolute temperature scale. This is made possible by the following property of the Carnot engine.

(a) It involves an adiabatic as well as an isothermal process.
(b) It is a cyclic process.
(c) It is most efficient engine operating between two given temperatures.
(d) It conserves energy.


Q12. A Carnot’s engine refrigerator taken heat from water at 0oC and discard it to a room at 27oC. What is the value of the co-efficient of its performance?

(a) 10.1
(b) 101
(c) 1.01
(d) 0.101


Q13. On a winter day, when the temperature outside is 17oC the temperature inside a room is maintained at 27oC by using a heat pump. The heat pump compensates for the loss of heat due to the difference of temperature. If, for the temperature given, the rate of heat loss is 6000 cal/s, what is the minimum rate of consumption of energy by the pump ?

(a) 840 watt
(b) 9300 watt
(c) 15000 watt
(d) 200 watt


Q14. An engine of efficiency η operates between two reservoirs at temperatures T1 and T2 with T2 > T1 doing an amount of work W in one cycle. All of this work used to drive an ideal Carnot engine in reserve (as a refrigerator) between the two reservoirs. The total heat extracted from the hot reservoir in one combined cycle of the two engines is :

(a) 0
(b) W( η+ T1/T2 – 1)
(c) – W( η + T1/T2 – 1)
(d) W( 1/η1/1 – T1/T2)


Q15. Using an engine of 30% thermal efficiency to drive a refrigerator having coefficient of performance of 5, what is the heat input into the engine for each MJ removed from the cold body by the refrigerator ?

(a) 6.6667 KJ
(b) 66667 KJ
(c) 66.667 KJ
(d) 666.67 KJ


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Answer Key (if you find any answer wrong, feel free to Correct us)

01.(a), (b), (d)06.(c)11.(c)
02.(a), (b), (d)07.(d)12.(a)
03.(a), (c)08.(b)13.(a)
04.(d)09.(c)14.(d)
05.(b)10.(a)15.(d)

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