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| Humidity |
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| Humidity is the amount of moisture (water vapor) present in the atmosphere. This moisture is due to the continuous evaporation of river, lakes, and oceans, and also from various life activities. |
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| At a given temperature, the maximum amount of water vapor that can be present is fixed. This is known as the saturated water vapor. If water vapor exceeds this limit it condenses and falls off as rain. For example, at 250C, the amount of saturated water vapor per cubic meter of air is 23 g only, at normal pressure. This maximum permissible amount of water vapor is also known as absolute humidity. Of course, absolute humidity increases with increase in temperature because of greater evaporation and also increase in pressure. At 400oC, the absolute humidity is 51 g per cubic meter of air. |
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| When the air is suddenly cooled the water vapor condenses into droplets. For example, dew drops on the leaves and grass can be observed early in the morning as a result of the condensation of water vapor in atmosphere due to sudden fall in night temperature. |
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