If we cant use metal in a microwave, why do they make the racks that come with the microwave metal, also in some microwaves the sides (on the inside) are metal too, how?
The sides are made out of metal because..
http://en.wikipedia.org/wiki/Faraday_cage
The trays can be used because they have no sharp pointy edges for sparks to build up on and the gaps are designed to be far enough apart so sparks can't bridge the gap (they also have to be far enough away from the edges otherwise sparks will jump across)
The trays can be used because they have no sharp pointy edges for sparks to build up on and the gaps are designed to be far enough apart so sparks can't bridge the gap (they also have to be far enough away from the edges otherwise sparks will jump across)