Prelims 2019 · Science and Technology · Question 84
Why are dewdrops not formed on a cloudy night?
Answer
Clouds reflect back the Earth's radiation.
- (a) Clouds do absorb some outgoing longwave radiation, but the key reason asked here is not mere absorption; it is that clouds send back this terrestrial radiation toward the surface. Not the best answer.
- (b) On clear nights, the ground loses heat rapidly by radiation and cools enough for dew formation. On cloudy nights, clouds reflect/re-radiate Earth's outgoing heat back, so the surface does not cool sufficiently to reach dew point. Correct.
- (c) Dew forms when the surface becomes cool; saying the Earth's surface has low temperature on cloudy nights is opposite to the actual effect. Incorrect.
- (d) Wind deflection is not the governing factor in dew formation here; the main process is nocturnal radiational cooling. Incorrect.