An alternating voltage applied to an aerial emits radio waves with the same frequency as the alternating voltage. When the waves are recieved they produce an alternating current in the aerial with the same frequency as the radiation recieved.
The radio and microwave spectrum is divided into different bands, which are used for different communication purposes.
The shorter the wavelength the more information they carry, the shorter their range, the less they spread out.
Mobile phones communicate with a local mobile phone mast using wavelengths just on the border between radio waves and microwaves. Some scientists think that the radiation from mobile phones may affect the brain.
Opitical fibres are very thin glass fibres. We use them to transmit signals carried by visible light or infrared radiation. The signals travel down the fibre by repeated total internal reflection.
Optical fibres carrying visible light or infrared are useful in communications because they carry much more information and are more secure than radio wave and microwave transmissions.
Comments
No comments have yet been made