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(a) Longdistance radio broadcasts use shortwave bands because only these bands can berefracted by the ionosphere.
(b) It is necessary to use satellitesfor long distance TV transmissions because television signals are of highfrequencies and high energies. Thus, these signals are not reflected by theionosphere. Hence, satellites are helpful in reflecting TV signals. Also, theyhelp in long distance TV transmissions.
(c) With reference to X-rayastronomy, X-rays are absorbed by the atmosphere. However, visible and radiowaves can penetrate it. Hence, optical and radio telescopes are built on theground, while X-ray astronomy is possible only with the help of satellitesorbiting the Earth.
(d) The small ozone layer on the top of theatmosphere is crucial for human survival because it absorbs harmful ultravioletradiations present in sunlight and prevents it from reaching the Earth’ssurface.
(e) In theabsenceof an 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 chilly anddifficult for human survival.
(f) A global nuclear war on thesurface of the Earth would have disastrous consequences. Post-nuclear war, theEarth will experience severe winter as the war will produce clouds of smoke thatwould cover maximum parts of the sky, thereby preventing solar light formreaching the atmosphere. Also, it will lead to the depletion of the ozonelayer.