The energy input to an engine is four times greater than the work it performs. What is its thermal efficiency?
Correct answer: C. 0.25
- A. 4.00
- B. 1.00
- C. 0.25
- D. Impossible to determine
Explanation
Thermal efficiency (η) is the ratio of useful work output to the total heat input (η = Work / Heatin). If Heatin = 4 × Work, then η = Work / (4 × Work) = 1/4 = 0.25. This corresponds to an efficiency of 25%.
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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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