Why does a microwave oven make a bulb light up?
Dear Straight Dope:
I heard a rumour once that if you put a light bulb (60w) into a microwave oven, in a bowl of water (just covering the metal), that the light would come on! Well, being the nut that I am, I tried it. To my surprise, the rumour was right! The light flickered on! I couldn't believe it! My question is ... how did that happen? I know you need some kind of current ... so how is that created?
This one is actually quite simple. Microwave ovens work by bombarding food with radio waves, right? And what happens when a radio wave goes past an antenna? You get a current through it. With me so far? Well, as far as the microwaves (the waves, not the oven) are concerned, the water and the filament and wires in the bulb are as good an antenna as any. You might ask (go ahead ... ask. You know you want to), "how does the electricity flow, if it has no ground?" The answer is, "induction, and microwaves going in every possible direction." One part of the wire might be getting zonked while another isn't, and even wire can store some static charge. The point is, the fluctuating magnetic field created by the microwave oven induces a current to flow, so the bulb lights up.