P4 Physics pg 95

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  • Radio waves and Microwaves
    • EM waves have different frequencies and act differently in the atmosphere
      • Below 30 MHz - radio waves are reflected of the ionosphere (waves travel longer)
      • Between 30 MHz and 30 GHz - radio/microwaves pass through atmosphere (transmissions must be in line of sight)
      • Above 30 GHz - microwaves are scattered  and absorbed by rain/dust (reduces strength of signal)
    • Dishes are used to receive microwaves signals
      • Normal tv/radio signals transmit using radiowaves which are recieved by an aerial
      • Use a dish as the wavelength of microwaves are too short for aerials
      • The dishes are a lot larger than the wavelenth, this reduces refraction and produces a narrow beam
    • Long wavelength radio waves diffract
      • Long wavelength radio waves have a large range (good for broadcasting)
      • Waves diffract when they pass through a narrow gap or past an object
        • The longer the wavelength of a wave, the more it will diffract (narrow gap = size of wavelength)

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