Q. Why are dewdrops not formed on a cloudy night?

• Clouds absorb the radiation released from the Earth’s surface.
• Clouds reflect back the Earth’s radiation.
• The Earth’s surface would have low temperature on cloudy nights.
• Clouds deflect the blowing wind to ground level.

Answer: (b) Clouds reflect back the Earth’s radiation.

Notes:

• When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew.
• The ideal conditions for its formation are
  • clear sky,
  • calm air,
  • high relative humidity, and 
  • cold and long night
• For the formation of dew, it is necessary that the dew point is above the freezing point.
• When the sky is clear and the trees and plants are cooler at nights, there is more evaporation of water and hence more dew formation.
• But when sky is cloudy, the trees and plants do not get cool in the night and hence there is less dew formation because on a cloudy night, the clouds send the heat (earth’s radiation) back to the ground so the ground never gets cold enough for the dew to be formed.