Microwaves are basically extremely high frequency radio waves, and are made by various types of transmitter.

In a mobile phone, they're made by a transmitter chip and an antenna, in a microwave oven they're made by a "magnetron".

Their wavelength is usually a couple of centimetres. Stars also give off microwaves.

Microwaves cause water and fat molecules to vibrate, which makes the substances hot.

So we can use microwaves to cook many types of food.

Mobile phones use microwaves, as they can be generated by a small antenna, which means that the phone doesn't need to be very big. The drawback is that, being small, they can't put out much power, and they also need a line of sight to the transmitter. This means that mobile phone companies need to have many transmitter towers if they're going to attract customers.

Microwaves are also used by fixed traffic speed cameras, and for radar, which is used by aircraft, ships and weather forcasters.

The most common type of radar works by sending out bursts of microwaves, detecting the "echoes" coming back from the objects they hit, and using the time it takes for the echoes to come back to work out how far away the object is.

Prolonged exposure to microwaves is known to cause "cataracts" in your eyes, which is a clouding of the lens, preventing you from seeing clearly (if at all!) So don't make a habit of pressing your face against the microwave oven door to see if your food's ready!

Recent research indicates that microwaves from mobile phones can affect parts of your brain - after all, you're holding the transmitter right by your head. Other research is inconclusive, although there is a feeling that you're more vulnerable if you're young and your brain is still growing.
So the advice is to keep calls short.
That's right - we're supposed to advise teenagers not to spend too long on the phone. What could possibly go wrong there?