How does a microwave work?

I bet that most of you never wondered how a microwave works. A staple appliance in our homes, microwaves has been around for a few decades now. Still, many people do not have the slightest idea about the mechanism how a microwave heats up and cooks food. When I was a kid, I used to think that microwaves were hot, just like a glass window of an oven is hot. Until I touched the microwave and found out, it is as cold as a window. Soon enough, I searched for books and asked around (there was not the internet back then) to find out how that is possible.

A microwave oven (microwave for short) works by exposing food to microwave radiation. Do not worry, even though it is called radiation, it is not harmful, at least not the level of radiation from a kitchen microwave oven. This type of radiation is called microwave because of it’s smaller wavelengths when compared to radio broadcasting wavelengths. The prefix „micro“ does not signify wavelength in the micrometer range. So, a microwave will emit microwave radiation into the food we eat, but why does the food get hot?

The physics of microwave cooking


When the food we put into the microwave oven is exposed to microwave radiation, the molecules in the food, specifically the polar molecules, start to jiggle around. This movement produces thermal energy, just like friction does in the macroscopic world. The whole process of releasing heat in this manner is called dielectric heating. For example, water is a typical polar molecule. Foods which contain a greater amount of water and are homogeneous will heat up more quickly compared to heterogeneous foods.

The invention and later history of microwave ovens

The credit for the invention of the first microwave ovens is usually given to Mr. Percy Spencer, right after the World War II. Spencer figured out that radar technology can be used for various other purposes and soon came up with the „Radarange,“ first sold in 1946. However, early microwave ovens were quite large and bulky and very difficult to use in an average kitchen. We had to wait until 1967 when the Amana Corporation introduced the standard, countertop microwave machine. Soon enough, these little ovens spread all over the world.


Nowadays, microwaves are most commonly associated with reheating foods which were cooked earlier and cooked various other foods. They come in very handy when some foods, which are usually prepared slowly, need to be rapidly heated, like butter, fats, and chocolate. However, extra caution is advised when heating up butter and fat in a microwave because these foods can attain very high temperatures.

Microwaves have found their way into the homes of millions, but professional cooks use them rarely. This is because microwave ovens work at lower temperatures than conventional ovens or pans and these can significantly impede the flavor release in the food. Housewives, on the other hand, love them when dinner needs to be reheated.