Humidity and Relative Humidity, Dew point, Mist, Cloud

Humidity

It is the water vapour content in the atmosphere. If there is high percentage of water in the air, the air is humid or moist.

Relative Humidity

It describes how moist the air is. It is defined as the ratio of the mass of water vapour present in a certain volume of air to the mass of water vapour required to saturate the same volume of air at the same temperature. It is expressed in percentage. Very high humidity or very low humidity makes one uncomfortable.

Measurement of Relative Humidity (Hygrometer)

Hygrometer is used to measure relative humidity. It consists of the dry bulb thermometer which reads temperature of dry air, and the wet bulb thermometer which records a lower temperature because evaporation of water from the  moist cloth cools the bulb. The lower the humidity, the lower the temperature of the wet bulb thermometer relative to the dry bulb thermometer. The difference between the two temperatures is high. If the humidity is high water evaporates slowly from the wet bulb. The difference between the two temperatures is small. The difference in the readings of the thermometers is a measure of the relative humidity.

Dew Point

It is the temperature at which the water vapour present in the air is just sufficient to saturate it.

Mist

They are condensed  water vapour( droplets)  suspended  in air near the earth surface when air have been  cooled below its dew point. Mist reduces visibility. In severe mist situation, we have fog.

Cloud

Cloud is a mass of small water droplets that float in the air. Cloud is high up in the atmosphere.

GENERAL EVALUATION ( POST YOUR ANSWER IN THE COMMENT BOX AT THE BOTTOM  FOR RATING AND DISCUSSION)

1. Explain the following terms: (i) Humidity (ii) Mist (iii) Dew point (iv) Cloud