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