Originally Posted by SmokeyTheBear

pasted:

In your microwave oven, there is no coax cable to connect the magnetron to the oven cavity. Instead, there is a rectangular box made of sheet metal. This is called a waveguide. It is roughly a U shaped, enclosed channel. The magnetron mounted is at one of the box (usually on the right side of the oven), and the other end of the box has what resembles a fan inside, called a "stirrer." This object is mounted just above the plastic or fiber cover you see inside the oven. A motor turns the stirrer slowly from outside the box. As microwaves from the magnetron travel down the inside of the box, they reach the stirrer and reflect off it. This scatters the energy around the inside of the oven. If your microwave oven only cooks or warms one small area of food you put in it and the rest of the food stays cold, it's likely the stirrer motor is no longer working. (It usually takes many years for this to happen.)

Microwaves are much like light. If you shine a flashlight (or "torch" for all of you European readers) at a mirror in your bedroom, light will bounce off it at exactly the same angle it strikes the mirror. What few people realize, is that microwaves do exactly the same thing with conductive surfaces.The better the conductor, the better these waves are reflected.