NewScientist The Last Word - Tag 'emptiness' details

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Where does the energy in empty microwave ovens go?

When I put baked beans in a jug in the microwave, and switch it on, the beans warm up, unsurprisingly. If I forget myself, overestimate the time needed, then shut the door with nothing in, then nothing warms up, because nothing is in there.

Where does the excess energy go? The electricity to generate the waves is being used regardless of whether there is anything to warm up or not. I understand that the waves will vibrate molecules in food if there is food there to warm, but what if there is nothing there to warm? I can hear the machine buzzing as it generates waves, so it is still using electricity, but what has happened to this energy?

Peter Finan

Haworth

West Yorkshire

(no votes)

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Answered by johneng
on 2010-09-17 16:47:23

(1 vote) average rating:4

the frequency of microwaves is the same as the resonate frequency of water. this means that the water in food absorbs the microwave energy well.

an analogy of this is pushing some one on a swing, if you push someone on a swing when they are moving away from you the go higher(warm up), this is resonance. if you just push randomly, sometime when coming towards you and sometimes when going away, you don't really achieve anything because all the pushing cancels out, but you are still using energy(this is like when the microwave just contains air).

this also works if you put a ceramic plat in the microwave, because all the water has been backed out it shouldn't be heated

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