How microwave ovens work

by Lisa Cardy

�

SILVER wants to know how microwave ovens work, so here's a whole article on the subject.

�

Microwave ovens are one of the twentieth century's great inventions and are found in most homes. They're popular for two main reasons: they cook food much quicker than conventional ovens AND because they only heat food and nothing else, they use electricity very efficiently.

�

The microwaves are actually radio waves. Most ovens use radio waves with a frequency of 2,500 megahertz (2.5 gigahertz). Radio waves in this frequency range have an interesting property: water, fats and sugars absorb them. When they are absorbed they are converted directly into heat.

�

It gets better, because plastics, glass and ceramics do not absorb the microwaves in this frequency. So the plate you put your potato on won't heat up, just the potato. However, metal reflects microwaves, so don't put saucepans in your microwave oven, it could cause an explosion.

�

Now for how food actually cooks. In a conventional oven heat has to migrate, via conduction, from the air inside the oven through the food being cooked. Which is why, if you don't get things placed right, your dinner will burn on the outside even though the inside may still be raw.

�

In microwave cooking, the radio waves penetrate the food and excite water and fat molecules, generating heat, pretty much evenly throughout the food. Heat doesn't need to be conducted through the food, it is everywhere at the same time, because all the molecules are excited in harmony.

�

Of course, in practise things aren't always this exact and the radio waves don't always evenly penetrate thick food. Also wave interference can result in 'hot spots' and it's always a good idea to stir food cooked in a microwave before eating it. But on the whole, heating food in a microwave is different from conventional cooking because molecules are excited and create heat, rather than heat having to be conducted.

�

Hope that clears everything up, but if I've missed anything then click here to add an answer.