Microwave Basics - How They Work
A small transmitting antenna, much like a radio station or TV station might use. The microwave oven converts the electricity from the house into an extremely high voltage, which feeds the "magnetron, " which converts the high voltage into electromagnetic wave energy, which is in the frequency band of radio waves.
The radio waves funnel into the cooking area of the oven, which makes the molecules in the food or liquid resonate (vibrate) wildly…which causes friction between the vibrating molecules…which generates the heat for cooking.
Wave guide and Stirrer blade
These work together to make sure the energy reaches all areas of the microwave oven interior.
Why some foods cook better than others
Whether a food type is suitable for cooking in a microwave oven has a lot to do with the structure of the food--or the lack of it:
Consider bread. It has an internal structure of air pockets. When the microwave gets all of the molecules in the structure vibrating at microwave frequency, the structures break down and the bread becomes tough and inedible if cooked too long.
Now consider water. It has no structure. When the microwave frequency gets the water molecules vibrating, they rub against each other creating friction--then heat. Because they have no fragile structures to break down, foods with high water content tend to heat nicely in the microwave--including vegetables, soups, and so on. Foods high in fat and sugar also, cook more quickly than other types.
Safe, quick, and inexpensive
Because microwave ovens use radio waves, rather than radiant heat, to heat food, they are considered to be quite safe. Also, they don't introduce anything unnatural into the food, and they are more energy efficient than standard resistance cooking devices.