An ideal heat engine has 100% efficiency only if its exhaust temperature is:
Correct answer: D. 0 K
- A. Less than input temperature
- B. Greater than input temperature
- C. Equal to input temperature
- D. 0 K
Explanation
c) Equal to input temperature:This option suggests that an ideal heat engine has 100% efficiency only if its exhaust temperature is equal to the input temperature. This is correct. According to the Carnot efficiency, the efficiency of an ideal heat engine is given by 1 - (T_low / T_high), where T_low is the exhaust temperature and T_high is the input temperature. The efficiency is maximum (100%) when T_low is equal to T_high.
This question appeared on the HEC Phase II 2017 paper, which you can sit online with every answer explained.
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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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