Define efficiency of a device in terms of energy input and useful output energy; show calculation example with numbers.

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Multiple Choice

Define efficiency of a device in terms of energy input and useful output energy; show calculation example with numbers.

Efficiency is the ratio of useful energy output to energy input, shown as a percentage. To work it out, divide the useful energy by the energy you put in, then multiply by 100%. For example, if a device uses 300 J of energy in and provides 100 J as useful output, the calculation is (100 / 300) × 100% = 33.3%. This is why 33.3% is the result in that scenario. If the numbers were different, you’d get other percentages: output 150 J from 300 J input gives 50%; output 60 J from 300 J input gives 20%; output 200 J from 300 J input gives 66.7%. Remember, efficiency cannot exceed 100% because you can’t get more useful energy out than you put in.

Efficiency is the ratio of useful energy output to energy input, shown as a percentage. To work it out, divide the useful energy by the energy you put in, then multiply by 100%.

For example, if a device uses 300 J of energy in and provides 100 J as useful output, the calculation is (100 / 300) × 100% = 33.3%. This is why 33.3% is the result in that scenario.

If the numbers were different, you’d get other percentages: output 150 J from 300 J input gives 50%; output 60 J from 300 J input gives 20%; output 200 J from 300 J input gives 66.7%. Remember, efficiency cannot exceed 100% because you can’t get more useful energy out than you put in.

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