Electromagnetic radiation ranges from the energetic x-rays to the less energetic radio frequency waves used in broadcasting. Microwaves fall into the radio frequency band of electromagnetic radiation. Microwaves should not be confused with x-rays, which are more powerful. Cooking with Microwaves Microwaves are produced inside the oven by an electron tube called a magnetron. The microwaves bounce back and forth within the metal interior until they are absorbed by food.
Microwaves cause the water molecules in food to vibrate, producing heat that cooks the food.
That's why foods high in water content, like fresh vegetables, can be cooked more quickly than other foods. The microwave energy is changed to heat as soon as it is absorbed by food. When thick foods like roasts are cooked, the outer layers are heated and cooked primarily by microwaves while the inside is cooked mainly by the slower conduction of heat from the hot outer layers. Microwave cooking can be more energy efficient than conventional cooking because foods cook faster and the energy heats only the food, not the oven compartment. Microwave cooking does not reduce the nutritional value of foods any more than conventional cooking.