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. Thus we can use microwaves to cookmany 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 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 cornea. 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. The current advice is to keep calls short.

People who work on aircraft carrier decks wear special suits which reflect microwaves, to avoid being "cooked" by the powerful radar units in modern military planes.