Answer the following
(a) Name the em waves which are suitable for radar systems used in aircraft navigation. Write the range of frequency of these waves.
(b) If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.
(c) An em wave exerts pressure on the surface on which it is incident. Justify.

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Solution

(a) Microwaves are suitable for radar systems used in aircraft navigation. The range of frequency for these waves is $10^{9} H z$ to $10^{12} H z .$
(b) In the absence of atmosphere, there would be no greenhouse effect on the surface of the Earth. As a result, the temperature of the Earth would decrease rapidly, making it difficult for human survival.
(c) An em wave carries a linear momentum with it. The linear momentum carried by a portion of wave having energy U is given by
p = U/c
Thus, if the wave incident on a material surface is completely absorbed, it delivers energy U and momentum p = Uc to the surface. If the wave is totally reflected, the momentum delivered is p = 2U/c because the momentum of the wave changes from p to -p. Therefore, it follows that an em waves incident on a surface exert a force and hence a pressure on the surface.

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