The Electro Magnetic Spectrum

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The Electro Magnetic Spectrum Radio Waves Radio waves are made by various types of transmitter, depending on the wavelength. They are also given off by stars, sparks and lightning, which is why you hear interference on your radio in a thunderstorm. Radio waves are the lowest frequencies in the electromagnetic spectrum, and are used mainly for communications. Radio waves are divided into:- [IMAGE]Long Wave, around 1~2 km in wavelength. The radio station "Atlantic 252" broadcasts here. [IMAGE]Medium Wave, around 100m in wavelength, used by BBC Radio 5 and other "AM" stations. [IMAGE]VHF, which stands for "Very High Frequency" and has wavelengths of around 2m. This is where you find stereo "FM" radio stations, such as "Galaxy 101" and "GWR FM". Further up the VHF band are civilian aircraft and taxis. [IMAGE]UHF stands for "Ultra High Frequency", and has wavelengths of less than a metre. It's used for Police radio communications, military aircraft radios and television transmissions. Large doses of radio waves are believed to cause cancer, leukaemia and other disorders. Some people claim that the very low frequency field from overhead power cables near their homes has affected their health. Microwaves 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 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.

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