. Discuss the Behaviour of atmosphere toward Electromagnetic wave
The behaviour of atmosphere is different for electromagnetic waves of different frequencies. The atmosphere is transparent to electromagnetic waves of visible region of wavelength range 4000Å to 8000Å, as we can see the sun and the stars through it clearly. The electromagnetic waves belonging to infrared region of wavelength range 8 10-7 m to 3 10-5 m are not allowed to pass through atmosphere rather they get reflected by atmosphere. The ozone layer of earth’s atmosphere blocks the electromagnetic waves of ultraviolet region of wavelength range 6Åto 4000Å. The behaviour of earth’s atmosphere towards electromagnetic waves of wavelength 10-10 m and higher is of special interest in space communication. The lower part of atmosphere is more or less transparent to electromagnetic waves of wavelength 20 m and higher used in radio communication but the top most layer, the ionosphere does not allow these waves to penetrate but reflects them back towards earth. Beyond a certain frequency, above 40 MHz, the ionosphere bends any incident electromagnetic wave but does not reflect it back towards earth.