A heat engine performs 100J of work and at the same time ejects 400J of heat energy to the cold reservoir. What is the efficiency of the engine?
Correct answer: A. 20%
- A. 20%
- B. 25%
- C. 4%
- D. 50%
Explanation
Total input energy = 100 + 400 = 500 J. Therefore % efficiency which is (Useful Work Done/Total Energy Input) x 100 = 100/500 x 100 = 20. Hence Option A is correct.
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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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