Vapour

Vapour is that gas which can be converted into liquid by applying pressure without changing temperature. A gas is different from vapours, gas cannot be converted into liquid by just apply pressure, to liquefy the gas high pressure and lower temperature is needed.

When the molecules of a liquid escape the liquid surface slowly, it results in vapour above the surface and this process is known as evaporation. Evaporation lowers the energy of a liquid and hence, causes cooling effect. This effect is used in cooling water in pitchers having porous walls; this is why water in earthen pot becomes cool.

Saturated: the space contain maximum possible amount of vapours

Unsaturated: the space contains less amount of vapour than maximum possible amount.

The possible maximum amount of vapour depends on the temperature & can be achieved easily due to rise in temperature of the liquid.

Saturation vapour pressure (SVP)= pressure exerted by saturated vapors

Dew point= the temperature at which saturated vapor pressure become equal to the present pressure is known as dew point. If the temperature is decreased below the dew point some of the vapour condenses.

Humidity

The amount of water vapor present in atmosphere is called humidity.

Absolute humidity= The amount of water vapour in a unit volume of air is called the Absolute humidity of air.

relative humidity=The ratio of the amount of water vapour present in a given volume to the amount of water vapour required to saturate the volume at the same temperature is called the relative humidity(R.H.).generally relative humidity present in percentage.

Dew: In winter nights, the atmospheric temperature goes down. The surfaces of window-panes, flowers, grasses etc. become still colder due to radiation. The air near them becomes saturated and condensation begins. The droplets condensed on such surfaces are called as Dew.

Fog: In winter, if temperature goes down even more, the whole atmosphere in that region may become saturated. Small droplets then condense on the dust particles present in the air. These droplets keep floating in the air & form a thick mist which restricts visibility. This thick mist is called Fog.

The human body is comfortable at a temperature between 23°C to 25°C at a relative humidity between 60% to 65%.air condition provide same.