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Idoh GerstenPhysicsIdoh GerstenMr ZambiziPhysicsMarch 12 1995Radio is a form of communication in which intelligence is transmitted without wires fromone point to another by means of electromagnetic waves Early forms of communication overgreat distances were the telephone and the telegraph They required wires between thesender and receiver Radio on the other hand requires no such physical connection Itrelies on the radiation of energy from a transmitting antenna in the form of radio wavesThese radio waves traveling at the speed of light 300000 kmsec 186000 misec carrythe information When the waves arrive at a receiving antenna a small electrical voltageis produced After this voltage has been suitably amplified the original informationcontained in the radio waves is retrieved and presented in an understandable form Thisform may be sound from a loudspeaker a picture on a television or a printed page from ateletype machineHISTORYEarly ExperimentersThe principles of radio had been demonstrated in the early 1800s by such scientists asMichael Faraday and Joseph Henry They had individually developed the theory that acurrent flowing in one wire could induce produce a current in another wire that was notphysically connected to the firstHans Christian Oersted had shown in 1820 that a current flowing in a wire sets up amagnetic field around the wire If the current is made to change and in particular madeto alternate flow back and forth the building up and collapsing of the associatedmagnetic field induces a current in another conductor placed in this changing magneticfield This principle of electromagnetic induction is well known in the application oftransformers where an iron core is used to link the magnetic field of the first wire orcoil with a secondary coil By this means voltages can be stepped up or down in valueThis process is usually carried out at low frequencies of 50 or 60 Hz Hertz or cyclesper second Radio waves on the other hand consist of frequencies between 30 kHz and 300GHzIn 1864 James Clerk Maxwell published his first paper
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