A reversible carnot engine converts 1/6th of heat into input work. When the temperature of the sink is reduced by 62°C, then the efficiency is doubled. The temperature of the source and sink is:
Correct answer: D. 99°C, 37°C
- A. 80°C, 37°C
- B. 99°C, 30°C
- C. 99°C, 25°C
- D. 99°C, 37°C
Explanation
The initial efficiency is η = 1/6 = 1 - Tsink /Tsource . When the sink temperature becomes Tsink - 62, the new efficiency is 2(1/6) = 1/3. Solving these two simultaneous equations gives Tsink = 310 K (37°C) and Tsource = 372 K (99°C).
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About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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