An ideal reversible heat engine is 100 efficient only if:
Correct answer: D. Cold reservoir is at 0 Kelvin
- A. Hot reservoir is at 0K
- B. Hot reservoir is at 0C
- C. Cold reservoir is at 0C
- D. Cold reservoir is at 0 Kelvin
Explanation
Cold reservoir at 0K: This is the only option that could theoretically allow for an ideal reversible heat engine to be 100% efficient. However, 0K is the absolute zero of temperature, and no heat can be extracted from a system at absolute zero.
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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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