Why are dewdrops not formed on a cloudy night?
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Answer: B. Dew forms when the ground cools enough at night for water vapour to condense. On a cloudy night, clouds send the Earth's outgoing heat back to the ground, so the surface stays warm and does not cool to dew point.
Watch for: Options A and B both sound right; the deciding idea is that heat returns to the ground, keeping it warm.
Why the other options are wrong
- A. Wrong because clouds absorb some radiation, but the key effect is sending heat back down to the surface.
- C. Wrong because cloudy nights are warmer, not colder, at the surface.
- D. Wrong because clouds do not push wind down to the ground.
Source to check: NCERT Class 11 Fundamentals of Physical Geography, Chapter 10 'Water in the Atmosphere' (Dew) and Chapter 8 (heat balance)
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.