Different electromagnetic eaves have different frequencies. This affects their properties and the effect that other materials have on them. Some frequencies can be used for transmitting information:
● Radio waves are used for transmitting radiation and television programmes because they are not strongly absorbed by the Earth’s atmosphere.
● They can travel long distances through the atmosphere and through space
● Radio telescopes are used in astronomy to pick up radio waves from stars
● Microwaves are used to transmit mobile phone signals because they are not strongly absorbed by the atmosphere
● They are reflected well by metals so satellite dishes are made of metal and shaped to reflect the signal onto the receiver
Light and infrared
● When it comes to I/GCSE Physics, Light and infrared radiation will travel huge distances down optical fibres without the signal becoming significantly weaker. This makes them very useful for carrying information, e.g. in computer networks and telephone conversations
For communication purposes, information can be superimposed onto an electromagnetic carrier wave to create a SIGNAL.
InI/GCSE Physics, Before a piece of information is transmitted, it is encoded in the transmitter in either an analogue or digital way. The receiver must then decode the signal to produce a copy of the original information
An ANALOGUE signal can vary continuously, so its amplitude can take any value:
Refer to I/GCSE Physics, A DIGITAL signal can only take one of a small number of fixed (discrete) – usually two. For transmitting information digitally, the digital code is made up of just two symbols – ‘1’ and ‘0’. Sounds and images can be transmitted digitally.
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