Consider the following statements with regard to atmospheric humidity:

1. Absolute humidity is the amount of water vapour per unit volume.

2. Hygrometer is used to measure relative humidity.

3. Dew point is the temperature at which the relative humidity is 75%.

Which of the above statements are correct?

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UPSC ESE 2018 Paper 1
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  1. 1 and 2 only
  2. 1 and 3 only
  3. 2 and 3 only
  4. 1, 2 and 3

Answer (Detailed Solution Below)

Option 1 : 1 and 2 only
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Detailed Solution

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  • Humidity is the amount of moisture (water vapor) in the air. It can be expressed as absolute humidity or relative humidity.
  • Hygrometer is used to measure the amount of humidity in the atmosphere.
  • Absolute humidity is the mass of water vapor divided by a unit volume of air (grams of water/cm3 of air).
  • Relative humidity is the amount of water vapour present in the air divided by the maximum amount that the air could contain at that temperature.
  • The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%.
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