What Is Humidity And Relative Humidity?

The air always contains some water vapour. When we keep ice cubes in a tumbler, water vapour in the atmospheric air condenses as water droplets on the outside of the tumbler. At a given temperature, there is a limit to the amount of vapour the air can support. When this limit is reached, the air is said to be saturated. At higher temperatures more water more water vapour is required to saturate the air.

Relative humidity is defined as the ratio of the mass of water vapour in a given volume of air to the mass required for saturating the same volume of air at the same temperature. The weather report in newspapers expresses relative humidity as percentage. Thus, if the relative humidity is 50 percent, the air contains half the amount it would contain when saturated at the same temperature. Relative humidity is measured with an instrument called hygrometer.

When the air contains large quantities of moisture, humidity is said to be high. Humidity depends on the moisture of the air at any given temperature there is a limit to the amount of moisture that the air can hold. When this limit is reached, the air is said to be saturated or at dew- point. Cold air can hold only relatively small quantities of water vapour before becoming saturated. However this amount increases rapidly as the temperature rises.
At normal atmospheric pressure at sea level.

An increase in temperature of about 10 Celsius doubles the air's moisture capacity. For example saturated at 18 Celsius contains twice as much moisture as saturated air at 7 Celsius. Therefore the amount of precipitation obtained from warm air is generally greater than that from cold air. The normal term used to express the amount of moisture in weather studies is relative humidity. This refers to the amount of water vapour in the air at a given temperature.  If the RH is 100% then the air is saturated. If the air contains only half the amount of water vapor that it can hold, the RH will be 50%.

Humidity and relative humidity mean the weather is a little wet , not dry and the contrary of 2 sides are also the same.