Question

what is relative humidity? How is it determined

Answer 1

Relative humidity is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature.
Relative humidity depends on temperature and the pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air.

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Answer 2

Relative humidity is the amount of water vapor (vapor pressure) that is in the air. It is a percentage of how much moisture the air could possibly holdThe higher the percentage of relative humidity, the more humid (moist) the air feels, while a lower percentage usually feels drier. Saturation occurs when air is holding the maximum amount of water vapor possible at the existing pressure and temperature. Saturation is equal to 100% relative humidity, resulting in precipitation.

A hygrometer is a device used for measuring the humidity of air. The humidity of an air–water vapor mixture is determined through the use of psychrometric charts if both the dry bulb temperature (T) and the wet bulb temperature (Tw) of the mixture are known.