We all learned early on not to put metal in the microwave. How dangerous is it, really? The answer is a confusing “it depends.”
Well, at a microscopic level most metals are lattice arrangements of atoms with a bunch of electrons freely floating around between them. The microwave radiation will attract all these electrons as it bounces around inside your microwave oven, pulling them back and forth, and this generates heat inside the metal. A large sheet of very thin metal, like a big piece of aluminum foil, can in fact heat up extremely rapidly, becoming so hot that it could start to burn the microwave. So don’t do that.
But the real danger comes from having metal with kinks or dead ends in it. That’s because as the electrons get shuffled back and forth, they will meet up with other electrons. This can create concentrated spots of negative charge. Electrons will naturally be repelled from areas where there is too much charge. If these negative spots happen to find themselves in a place where they are near air, like in the tines of a fork or a kink in crumpled aluminum foil, the electrons will jump away, creating a spark and ionizing the air molecules into a plasma.
That sounds awful, but there are some pieces of metal that ares okay in the microwave. Wired explains the differences between safe and unsafe metals, but since it’s a bit complicated, we all tell our children not to put any metal in the microwave or some mysterious horrible thing will happen. -via Digg