Which measure of humidity, relative humidity or dew point, best ...

[HudsonKB16]

Which measure of humidity, relative humidity or dew point, best describes the actual quantity of water vapor in a mass of air?
 
  What will be an ideal response?

Question 2

Briefly describe the principle of a psychrometer.
 
  What will be an ideal response?

[bitingbit]

Answer to Question 1

Dew-point temperature is a measure of the air's actual moisture content.

Answer to Question 2

A psychrometer is used to determine the moisture content of the air using wet-bulb and dry-bulb thermometers. The dry-bulb thermometer measures air temperature. The wet-bulb thermometer has a cloth wick that is saturated with water, and when a current of air passes over it, the water evaporates. As it evaporates, the water absorbs heat energy, causing the temperature to drop. The amount of cooling is directly proportional to the dryness of the air, as drier air will result in a larger amount of evaporation and resultant cooling. Therefore, the larger the difference in the wet-bulb and dry-bulb temperatures, the lower the relative humidity.