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Comparing propagation in free space with propagation in sea water at 1 MHz, the wave in sea water

  • A.does not propagate at all
  • B.is attenuated severely within a fraction of a metre
  • C.travels faster and further than in free space
  • D.is unattenuated but travels more slowly

Answer: B

Sea water is a good conductor at a megahertz and the skin depth is of the order of a quarter of a metre, so the field falls by a factor of e in that distance. Communication with a submerged submarine therefore uses very low frequencies, where the skin depth is tens of metres.

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