Give Now

A Moment of Science

How Do Microwaves Heat Up Food?

Have you heard the phrase, "Let's nuke it in the microwave!" Well, Nuclear power and microwaves really don't have much in common.

retro microwave oven

Photo: jmv (flickr)

Microwave ovens heat up water to cook food.

“Let’s nuke it in the microwave,” we often say as we pull a frozen dinner out of the freezer. That figure of speech seems to express the fact that our experience with nuclear power and with microwaves goes back only a few years, while our experience with fire goes back thousands of years.

We seem to be reacting to the novelty that nuclear power and microwave cooking have in common. They don’t really have anything else in common.

Microwave History

Microwaves are electromagnetic waves, exactly the same as visible light except that microwaves have much longer wavelengths than the light our eyes detect. The first large-scale use of microwaves was in radar in the 1930′s. Now microwaves are also used to transmit telephone and television signals.

Microwaves cook food by heating the liquid water it contains. Even frozen food contains some liquid water, at least on the outside surface exposed to warm air on the way from the freezer to the oven.

How Do Microwaves Work?

Microwaves heat water by jerking the water molecules around, so to speak. Each water molecule has a slight positive electric charge on one side and a slight negative charge on the other.

As microwaves pass by, they exert forces on those charges, first one way, then the other, several billion times per second.

Microscopic Stirring

These back-and-forth forces turn the water molecules one way, then the other, repeatedly breaking the temporary bonds that water molecules form with each other. It’s a kind of microscopic stirring.

The result of all this agitation is more violent random motion of all the water molecules in the food — in other words, the water gets heated.

Microwaves reach all the water in the food at once, so all parts of the food are heated at once. A conventional oven heats food only from the outside, and that’s why conventional cooking takes longer than microwave cooking.

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science