Physics · Energy. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Power is how quickly energy is transferred. A device with more power transfers the same energy in less time. One watt is one joule every second.
Energy cannot be created or destroyed. It can only be transferred usefully, stored or dissipated. Dissipated energy spreads out into the thermal store of the surroundings, where it is no longer useful. We call this wasted energy. Every real change wastes some energy, usually because of friction or heating.
Efficiency tells you what fraction of the input energy ends up where you want it. Lubrication reduces friction and thermal insulation reduces heating of the surroundings, so both cut the waste.
Students divide the input by the useful output and get an efficiency bigger than 1. The useful output always goes on top, and the answer must be 1 or less (100% or less).
Answer: 0.60 (60%)
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