Telecommunications: Communication Using Cables
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how is sound converted in a telephone?
- sound is converted directly into an electrical signal at the mouthpiecewhich is then sent along a wire to an earpiece
- where it is converted back into sound
in a telephone, what energy conversions take place?
- the mouthpiece contains a microphone, which converts sound into electrical energy
- the earpiece contains a loudspeaker, which converts electrical energy into sound energy
what is an optical fibre?
a long, thin thread of glass through which light can travel
advantages of optical fibres are: (know 4)
- smaller in size
- cheaper to make
- greater signal capacity
- higher signal quality
- less energy loss per km
- not affected by interference
- not easily tapped
what is the law of reflection?
when light is reflected from a plane mirror it is found that the angle of incidence is equal to the angle of reflection
one disadvantage of optical fibres is?
- light signals only travel at 2x108
- as opposed to almost 3x108 for electrical signals in a wire
what is the principle of reversiblity?
if the direction of a ray of light is reversed it will follow the same path, but in the opposite direction
why do optical fibres work?
- because of total internal reflection
- this is when all the light is reflected inside the glass and none escapes into the air
- total internal reflection occurs when the angle of the incident ray is greater than an angle known as the critical angle
- in this way light can travel great distances through optical fibres without ever leaving the fibre
what happens in an Optical Fibre Transmission System?
- electrical signals are converted into pulses of light by laserthese pulses of light then travel down the optical fibre and at the other end are converted back into electrical signals by a photodiodethe laser and photodiode are so fast acting that hnudreds of different signals can be transmitted down the same fibre simultaneously
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