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A machine has an efficiency of 80%. What percentage of energy is lost?

April 15, 2026Physics

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Answer

2 steps

Understand the concept of efficiency.
Efficiency is the percentage of input energy that is converted into useful output energy. The remaining percentage of energy is lost, usually as heat or sound.
Calculate the percentage of energy lost.
If a machine has an efficiency of 80%, it means 80% of the energy input is converted into useful work. The energy lost is the difference between the total input energy (100%) and the efficiency.
$\text{Percentage lost} = 100\% - \text{Efficiency}$ $\text{Percentage lost} = 100\% - 80\%$ $\text{Percentage lost} = 20\%$
The machine loses 20% of the energy.

The correct option is C.

\boxed{\text{C. 20%}}

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