Standard Science Primary 6 Energy

Why is it impossible for a machine to be 100% efficient in converting energy?

A Some energy is always destroyed.
B Energy cannot be created.
C Some energy is always converted into non-useful forms like heat.
D Potential energy cannot be fully converted to kinetic energy.
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Worked Solution

Step 1: During energy conversion, friction and electrical resistance occur. Step [2-9]: This causes some energy to be transformed into heat or sound. Step [2-9]: Since these forms aren't the intended "useful" output, efficiency is never 100%.

Correct answer: Some energy is always converted into non-useful forms like heat.

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