Radio waves

Stars are natural images of radio waves. However, radio waves can be produced artificially by making a current oscillate in transmitting aerial (antenna). In a simple radio system a microphone controls the current it to the aerial so that the radio waves  'pulsate'. In the radio receiver, the incoming pulsations control a loudspeaker so that it produces a copy of the original sound. Radio waves are also used to transmit TV pictures.



Long and medium build disffract (bend) around hills, so radio can still receive signal even if a hill blocks the direct route from the transmitting aerial. Long waves will also diffrat the curving surface of Earth.

VHF and UHF waves have shorter wavelengths. VHF (very high frequency) is used car stereo radio and UHF (ultra high frequency) for TV broadcasts. These days do not diffract around hills. So, for good reception, there needs to be a straight path between the transmitting and recovering aerials.

Microwaves have a shortest wavelengths ( and highest frequencies) of radio waves. They are used by mobile phone, and beaming TV and telephone signals to and from satellites and across the country.

Like all electromagnetic waves, microbeads produce a heating effect then absorbed. Water absorbs microwaves of one particular frequency. This principle is used in microwave ovens, when the waves penetrate deep into food and heat up the water in it. However, if the body is exposed to microwaves, they will cause internal heating of body tissues.