The Telephone

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The Telephone
transmitter
loudspeaker
(Sound energy to electrical energy)
(Electrical energy to sound energy)
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Printed circuit board of the telephone
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An Older Telephone
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Using an oscilloscope
1) Quiet sound, low frequency
2) Quiet sound, high frequency
3) Loud sound, low frequency
4) Loud sound, high frequency
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Telecommunication Optical Fibres

• The law of reflection.
• When a ray of light bounces off a mirror , the
  angle going in equals the angle coming out.
• The line at right angles to the mirror is called
  the normal.

6
Optical Fibres

• When light is incident on a glass surface,
  refraction or bending of the light takes place.
• The light comes out of the glass.
• This however is dependent on the angle i.

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Finding the Critical Angle
1) Ray gets refracted
2) Ray still gets refracted
4) Ray gets internally reflected
3) Ray still gets refracted (just!)
8
Optical Fibres

• Optical fibres are made of thin flexible glass
  threads.
• They are about the size of a human hair.
• The fibres have a protective coating which keeps
  the light inside the fibre.

9
Satellites

• Interactive summary.
• Satellites which orbit the earth every 24____
  are called ________ satellites.
• They are above the _____ point on the _____ .
• Satellites use ______ dishes to _______ the
  microwave signals.
• The microwave signals travel in _______ lines.

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