Question

Which is the cause of Greenhouse effect?
(A) Infrared rays
(B) Ultraviolet rays
(C) X-rays
(D) Radio waves

Answer 1

Hint: This effect is caused when radiation energies incident towards the earth are radiated by the greenhouse gases towards the surface, absorbed by the atmosphere and some reflected back. The energy absorbed by the earth’s surface and converted to heat energy. This leads to an increase in the temperature of the earth’s surface.

Complete step by step answer:
-First of all we will see what the greenhouse effect is.
The greenhouse effect is basically the phenomenon where radiation from the earth’s atmosphere heats up the earth’s surface to very higher temperatures than normal.
The greenhouse gases or the radiatively active gases like water vapour, carbon dioxide ($C{O_2}$), methane ($C{H_4}$), nitrous oxide (${N_2}O$) and ozone (${O_3}$) in the earth’s atmosphere radiate heat energy in all directions. Some part of these radiations is also directed towards the earth’s surface, this will lead to the surface being heated up. The rate of heating of the earth’s surface depends on the temperature of the atmosphere and the amount of the greenhouse gases present in the atmosphere.
-We can understand the above concept in the following manner:
The sun releases UV, infrared and visible radiation which is received by the earth. The atmosphere and the clouds redirect back most of the incoming solar radiations from the sun; some of it is absorbed by the clouds and atmosphere while the rest of it gets absorbed by the earth’s surface. This part of the radiation absorbs, heats up the surface and gets converted into heat. All this leads to an increasing temperature of the earth. This is known as global warming.
-The greenhouse gases present in the atmosphere absorb more of the infrared radiations as compared to UV, X and radio waves, which are unable to escape the atmosphere and cause the temperature of the earth to rise, resulting in a greenhouse effect.

Hence the correct option will be: (A) Infrared rays

Note: The greenhouse gases contribute differently to the greenhouse effect: water vapour = 36 – 70 %, carbon dioxide ($C{O_2}$) = 9 – 26 %; methane ($C{H_4}$) = 4 – 9 %; ozone (${O_3}$) = 3 – 7 %. The greenhouse effect can be natural as well as man-made (anthropogenic) when human activities lead to increase in the concentration of greenhouse gases. The greenhouse effect leads to global warming, depletion of ozone layer, smog and air pollution, acidification of water bodies, etc.