Why Doesn't the Inside of an Empty Microwave Oven Get Hot?

Microwave Oven Components

• All microwaves have four basic components. The outer shell and cooking chamber provide structure for the oven. The operating console is a switch that typically controls the cooking time and microwave frequency. Behind the console are the high-voltage transformer and magnetron. The transformer boosts the incoming electrical current supplied to the magnetron. The magnetron is a specialized vacuum tube that transforms electricity into microwave radiation.

Microwave Radiation

• Microwaves are a form of electromagnetic (EM) energy or radiation. Like other forms of EM radiation, microwaves consist of discreet bundles of energy called photons that travel through a vacuum at the speed of light. Microwave radiation includes EM energy with frequencies between 1 and 300 GHz.

Microwave Interactions

• Depending on the type of matter encountered by microwaves, they can be transmitted, reflected, refracted, absorbed or attenuated (partially absorbed). Dry air in your microwave oven allows transmission of the microwave radiation without imparting a significant amount of energy to the air molecules. If steam has collected in the cooking chamber from cooking food, however, microwave energy will interact with the water molecules in the chamber.

How Food Cooks in a Microwave Oven

• Three types of energy transformation must occur to cook food in your microwave oven. Incoming electrical current is transformed into microwave radiation in the magnetron. When the microwaves interact with the food, the food molecules become physically agitated, transforming EM microwave energy into kinetic (movement) energy. Friction between the moving food molecules generates thermal energy or heat, which cooks the food.