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Dew Point Explained !!

                                             Why do cold drinks sweat in hot weather ?



The dew point is the temperature at which water vapour condenses into liquid water , ie. it is the temperature at which the air can no longer "hold" all of the water vapor which is mixed with it, and some of the water vapor must condense into liquid water.
The dew point is a reflection of the humidity. The dew point of humid air will be higher than the dew point of dry air. When air has reached the dew-point temperature at a particular pressure, the water vapor in the air is in equilibrium with liquid water, meaning water vapor is condensing at the same rate at which liquid water is evaporating.




Below the dew point, liquid water will begin to condense on solid surfaces (such as blades of grass) or around solid particles in the atmosphere (such as dust or salt), forming clouds or fog.
In technical terms, the dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. The condensed water is called dew when it forms on a solid surface, or frost if it freezes. In the air, the condensed water is called either fog or a cloud, depending on its altitude when it forms. 
A higher dew point means there is more moisture in the air. A very high dew point can indicate severe weather. A high dew point means that the air is unstable and that thunderstorms may develop. Also While relative humidity is a relative measure of how humid the air is, the dew point temperature is an absolute measure of how much water vapor is in the air.
Increasing the barometric pressure increases the dew point. This means that, if the pressure increases, the mass of water vapor in the air must be reduced in order to maintain the same dew point. 
Water will condense as liquid on any surface that has a temperature below the dew point. If the surface temperature of your cold glass is below that of the dew point, you will have water condensing on it. The exact same sequence of events causes dewdrops to form on plant leaves.

                                                 

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