Telecommunications: Communication Using Cables

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Author:
crobertsonx
ID:
86651
Filename:
Telecommunications: Communication Using Cables
Updated:
2011-05-18 20:24:30
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Telecommunications Communication Using Cables physics
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Telecommunications: Section 2- Communication Using Cables
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  1. how is sound converted in a telephone?
    • sound is converted directly into an electrical signal at the mouthpiece
    • which is then sent along a wire to an earpiece
    • where it is converted back into sound
  2. 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
  3. what is an optical fibre?
    a long, thin thread of glass through which light can travel
  4. advantages of optical fibres are: (know 4)
    • smaller in size
    • cheaper to make
    • lighter
    • greater signal capacity
    • higher signal quality
    • less energy loss per km
    • not affected by interference
    • not easily tapped
  5. 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
  6. one disadvantage of optical fibres is?
    • light signals only travel at 2x108
    • as opposed to almost 3x108 for electrical signals in a wire
  7. 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
  8. 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
  9. what happens in an Optical Fibre Transmission System?
    • electrical signals are converted into pulses of light by laser
    • these pulses of light then travel down the optical fibre and at the other end are converted back into electrical signals by a photodiode
    • the laser and photodiode are so fast acting that hnudreds of different signals can be transmitted down the same fibre simultaneously

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