Question

The time of the day when relative humidity reaches a maximum value is usually.
A. At the time when the air temperature is highest
B. In the middle of the afternoon
C. At the time when the air temperature is lowest
D. Just before sunrise

Answer 1

Relative humidity is the ratio of the partial pressure of water vapour to the water vapour pressure at a given temperature. It depends upon pressure and temperature. If the relative humidity is 100% then it means that the air is saturated totally with water vapour and cannot hold it in anymore which causes rain.

Step by step answer: Option A- At the time when the air temperature is highest
When the air temperature increases, the relative humidity decreases as air can hold more water molecules with the temperature being high. So warmer the air more will be water molecules held.
Option B- In the middle of the afternoon
It is the hottest during the middle of the afternoon as more heat arrives at the earth from the sun than leaving. This causes low relative humidity.
Option C- At the time when the air temperature is lowest
When the air temperature decreases, the relative humidity increases due to saturation of air with water molecules. The lower the temperature, the more will be the chances of precipitation due to high relative humidity.
Option D- Just before sunrise
The temperature drops just before the sunrise as more heat leaves the earth than arriving due to the absence of a source of heat i.e., the sun.
Thus, the correct option is option C- At the time when the air temperature is lowest.

Note: The point where the relative humidity reaches 100 % is called a dew point as dew formation takes place. When the warmer air starts to cool down, the air loses water vapour in the form of condensation. Higher the dew point, the higher will be the moisture content in the air which leads to humidity with clouds and might cause precipitation.