The efficiency of a machine is
Correct answer: B. the ratio of useful output energy to total input energy, expressed as a percentage
- A. always greater than 100 per cent
- B. the ratio of useful output energy to total input energy, expressed as a percentage
- C. the ratio of input to output
- D. equal to the power output
Explanation
Efficiency can never exceed 100 per cent, because energy is conserved and some is always lost to friction, sound and heat. An electric motor may reach 90 per cent while a petrol engine manages only about 25 per cent. The wasted energy is not destroyed, merely converted into forms that are not useful.
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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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