How are infrared waves produced? Why are these referred to as 'heat waves’? Write their one important use.
Infrared waves are produced by hot bodies and molecules.
They are referred as heat waves because they are readily absorbed by water molecules in most materials, which increase their thermal motion, so they heat up the material.
Infrared waves are used for therapeutic purpose and long distance photography.
Name the parts of the electromagnetic spectrum which is
(a) suitable for radar systems used in aircraft navigation.
(b) used to treat muscular strain.
(c) used as a diagnostic tool in medicine.
Write in brief, how these waves can be produced.To which part of the electromagnetic spectrum does a wave of frequency 5 x 1019 Hz belong?
The part of the electromagnetic spectrum is X-rays.
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.(a) Microwaves are suitable for radar systems used in aircraft navigation. The range of frequency for these waves is 109 Hz to 1012 Hz.
(b) There would be no greenhouse effect on the surface of the Earth in the absence of atmosphere. As a result, the temperature of the Earth would decrease rapidly, making it difficult for human survival.
(c) When the wave is incident on the metal surface, it is completely absorbed. Energy U and hence momentum (p = 
is delivered to the surface of the earth. The momentum delivered becomes twice when, the wave is totally reflected because momentum is changed from p to –p. Thus, force and thereby pressure is exerted on the surface of the earth by EM waves.
Switch
) will remain same in vacuum. 
