Telecommunication Answers
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  1. a) Light travels much much faster than sound. Speed of sound = 340m/s. Speed of light = 300,000,000m/s. b) Using the formula distance = speed x time we get 340 x 3 = 1020m
  2. In the telephone it is the microphone that changes the sound from your voice into the electrical signal that is then transmitted through the phone wires.
  3. In the diagram there are two complete waves on the screen so if the frequency is doubled the new picture will contain four complete waves as shown in the diagram
    oscilloscope
  4. The diagram has two whole waves covering 24m therefore one wavelength must be 12m. using the formula wave speed = frequency x wavelength,
    ie, v = f x we get 8 = f x 12 so f = 8/12 = 0.67Hz.
  5. The names in the blocks are:
    blocks
  6. Use the formula v = f x . You must remember that radio waves belong to the electromagnetic family of waves and all such waves travel at the speed of light in air . So putting in the numbers we get : 300,000,000 = 909,000 x
    therefore = 300,000,000 / 909,000 = 330m.
  7. Long waves are better at bending around obstacles such as buildings than short waves. That is why it is difficult to receive good television pictures when your house is in the shadow of a large building or a hill. The diagram below shows this bending of long & short waves which is called diffraction.
    diffraction
  8. Radio waves cannot pass through metal boxes which is what a car is basically! So an outside aerial is need to take the signal inside the car. Try wrapping tin foil around your portable radio. Do you get reception?
  9. A geostationary satellite takes 24 hours to go round the planet. This exactly matches the time it takes for the earth to spin round once. So the satellite appears to be above one spot all the time hence the name… geo (place) stationary (still). The time for the satellite to make a complete orbit is called its period. Geostationary satellites orbit at a distance of 35,900 km.
  10. An optical fibre is like a thin thread of glass. The light passes down the fibre by a process called total internal reflection.
    fibre


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