The energy input to an engine is 60J, and the work it performs is 15J. 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 the useful work output to the total energy input. Here, η = Work / Energyinput = 15 J / 60 J = 1/4 = 0.25. This corresponds to an efficiency of 25%.
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About Energy Losses and Efficiency
Efficiency compares useful output energy or power with the total input, usually expressed as a percentage. The topic covers energy losses through friction, heating, resistance and sound, along with power ratings and Sankey diagrams. Efficiency is not the same as conservation of energy, because lost energy is transferred rather than destroyed.
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