Answer the following questions:
(a) Long distance radio broadcasts use short-wave bands. Why?
(b) It is necessary to use satellites for long distance TV transmission. Why?
(c) Optical and radiotelescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why?
(d) The small ozone layer on top of the stratosphere is crucial for human survival. Why?
(e) If the earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now?
(f) Some scientists have predicted that a global nuclear war on the earth would be followed by a severe ‘nuclear winter’ with a devastating effect on life on earth. What might be the basis of this prediction?

Explanation

(a) Ionosphere reflects waves in these bands.
(b) Television signals are not properly reflected by the ionosphere (see text). Therefore, reflection is effected by satellites.
(c) Atmosphere absorbs X-rays, while visible and radiowaves can penetrate it.
(d) It absorbs ultraviolet radiations from the sun and prevents it from reaching the earth’s surface and causing damage to life.
(e) The temperature of the earth would be lower because the Greenhouse effect of the atmosphere would be absent.
(f) The clouds produced by global nuclear war would perhaps cover substantial parts of the sky preventing solar light from reaching many parts of the globe. This would cause a ‘winter’.