Previous Year Question
With reference to the Earth’s atmosphere, which one of the following statements is correct?
The total amount of insolation received at the equator is roughly about 10 times of that received at the poles.
Infrared rays constitute roughly two-thirds of insolation.
Infrared waves are largely absorbed by water vapour that is concentrated in the lower atmosphere.
Infrared waves are a part of the visible spectrum of electromagnetic waves of solar radiation.
Correct Answer: C
Detailed Solution
Option (c) is correct. Water vapour is one of the most important natural greenhouse gases in the Earth’s atmosphere. Most atmospheric water vapour is found in the troposphere, which is the lower part of the atmosphere.
After absorbing solar energy, the Earth’s surface re-emits it as long-wave infrared radiation. Water vapour present in the lower atmosphere absorbs a large part of this infrared radiation and re-radiates it.
Option (a) is incorrect. The equator receives more insolation than the poles because the Sun’s rays strike it more directly. However, the total insolation received at the equator is not approximately ten times that received at the poles.
Option (b) is incorrect. Infrared radiation forms an important part of solar energy, but it does not constitute approximately two-thirds of insolation. Solar energy includes visible light, infrared radiation and ultraviolet radiation.
Option (d) is incorrect. Infrared radiation has wavelengths longer than visible red light in the electromagnetic spectrum. Therefore, it is not a part of the visible spectrum.