When you place food in the microwave, you are actually cooking it by creating an electric current that changes the heat content of the food. This current causes the food to produce heat in the microwave oven, which cooks the food by turning it from a solid into a gas, which allows heat to flow. Since the heat is no longer being created in the microwave oven, the food does not cook as fast as it would if the heat had not been transferred to the food. Most microwaves heat food up to between 3 and 4200 degrees Fahrenheit.
Microwaves heat the food by altering the temperature of the air in the oven cavity. Air is about 0 degrees Celsius, and microwaves heat it to about +380 degrees Celsius. A standard oven uses a convection oven with 1 inch of hot air. A "smart" convection-style microwave oven has a special heating element that does not need a preheating fan.
Microwave radiation, the way microwaves heat up food, is not enough to cook food without help. Microwave radiation is an electromagnetic wave, and the wave carries only electromagnetic energy. The wave can not carry heat, so you need to use another method of heat transfer to make your food cook.
At low power levels, the energy in microwaves is about 3 milliwatts. The wave does not penetrate far enough into the food to be effective. At higher levels, the amount of energy in the wave increases to about 6 milliwatts. The microwave oven heat exchanger is used to heat food between these two power levels. This heat exchanger does not get very hot, because the microwaves are not powerful enough to heat a normal oven. In a typical microwave oven, the heating element heats the food at about 350 degrees Celsius. The air in the oven cavity warms the food to about +350 degrees Celsius, which is about 2.5 times the temperature of the food. This increases the food's temperature enough to cook it. The excess heat in the air becomes part of the microwave oven's current, and causes it to heat the air even more. The amount of heat gained in this way causes the food to cook at a fast rate.
A microwave oven works in a very similar way to a stove. When you put food on the stove, heat is transferred from the food to the heat exchanger. The food is the same in both processes: it needs heat and it is burnt by heat. In the microwave oven, the heat is transferred from the food to the heat exchanger. The heat exchanger uses the extra heat in the microwave oven to heat the oven.