PRESENTED BY-PRESENTED BY-

PRATEEK PRATEEK

SOME DEFINATIONSSOME DEFINATIONS Evaporation:- conversion of a liquid to a vapour.

Transpiration:- that part of evaporation which enters the

atmosphere through plants.

Total Evaporation:- the combined processes of evaporation and

transpiration .

this has been referred to as evapotranspiration.

EVAPORATIONEVAPORATION Evaporation is a type of vaporization of a liquid that occurs

from the surface of a liquid into a gaseous phase.

REASON FOR EVAPORATIONREASON FOR EVAPORATION

FACTORS AFFECTING FACTORS AFFECTING EVAPORATIONEVAPORATION Various factors affecting the rate of evaporation

are:-

1)Concentration of the substance evaporating in the air.2)Concentration of other substances in the air.3)Temperature of the substance.4)Flow rate of air.5)Inter-molecular forces.6)Surface area and temperature.7)Humidity.

FACTORS AFFECTING FACTORS AFFECTING EVAPORATIONEVAPORATION1. Concentration of the substance

evaporating in the air.

If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.

FACTORS AFFECTING FACTORS AFFECTING EVAPORATIONEVAPORATION2) Concentration of other substances in the

air :-

If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating. I.e.. The rate of evaporation of substance is less.

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FACTORS AFFECTING EVAPORATIONFACTORS AFFECTING EVAPORATION3) Temperature of the substance.:- If the substance is hotter, then evaporation will be faster.

As the temperature of air is increased, its capacity to hold moisture also increases.

Increase in air temperature provide more energy to molecule to change its state. Hence evaporation is directly proportional to the temperature of evaporating surface.

Warmer the evaporating surface, higher the rate of evaporation

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FACTORS AFFECTING EVAPORATIONFACTORS AFFECTING EVAPORATION

4). Flow rate of air :- Molecules in motion have more energy than those at

rest, and so the stronger the flow of air, the greater the evaporating power of the air molecules.

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FACTORS AFFECTING EVAPORATIONFACTORS AFFECTING EVAPORATION 5). Inter-molecular forces The stronger the forces keeping the molecules together in

the liquid or solid state the more energy that must be input in order to evaporate them.

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FACTORS AFFECTING FACTORS AFFECTING EVAPORATIONEVAPORATION 5). Surface area and temperature

The rate of evaporation is determined by the area of the exposed surface of water. Larger areas of evaporating surface increase the rate of evaporation.

A larger surface area allows more molecules or atoms to leave the liquid, and evaporation occurs more quickly.

For example, the same amount of water will evaporate faster if spilled on a table than if it is left in a cup.

FACTORS AFFECTING FACTORS AFFECTING EVAPORATIONEVAPORATION 5). Humidity

The rate of evaporation is closely related with the relative humidity of air.

the moisture holding capacity of air at a given temperature

is limited, drier air evaporates more water than moist air .

In other words, higher the vapour pressure, lower the rate of evaporation.

It is a common experience that evaporation is greater in summer and at mid-day than in winter and at night.

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