What does the percentage of humidity mean?

Question

for example, the weather report says it will be 20% humidity

Answer 1

Vapor Pressure/Equilibrium Vapor Pressure

Vapor Pressure is the pressure of the water vapor in the air.
Equilibrium Vapor Pressure is when the Vapor Pressure is at equilibrium with condensation and evaporation. Equilibrium Vapor Pressure is also the Vapor Pressure at the dewpoint.

A change in the vapor pressure results in either more evaporation or condensation. Higher temperature makes more evaporation because the vapor has more outwards pressure and lower temperature makes more condensation because it has less outward pressure. When these are equal, it is the dewpoint.

Air does not have a capacity for holding water vapor that changes with temperature. This is a common but erroneous belief. Air doesn't even hold water vapor, it is just there.

20% humidity means that there is 20% of the water vapor in the air necessary for condensation to become equal to evaporation at the given temperature and therefore have reached the dewpoint.

Answer 2

It means that 20% of the possible water vapor the air will hold. It is actually is computed from the dew point which is the temperature at which moisture condenses out (100%) on a chilled metal plate but it can be roughly measured by connecting a hair which expands and contracts with humidity and can be made to pull a needle across a dial. There are now solid state sensors to measure it and it used to be that by wetting a sleeve on one thermometer and slinging it around with a dry one, one got two temperatures and could look up the humidity in a table.

Answer 3

The maximum amount of water vapour air can hold varies with temperature.For a particular temperature,if air is holding the maximum possible water vapour, then the air becomes saturated.This means if you try to add some more moisture, air cannot hold it and the excess water vapour condenses as water droplets to form clouds.In this condition the air is said to have 100 percent relative humidity.Therefore the relative humidity is known as the degree of saturation.
In short the relative humidity is defined as the ratio of of the amount of water vapour present in the air to the amount of water vapour required to saturate it at that temperature.If there is 20 percent humidity,it means that the air is having only 20 percent even though it can hold 100 percent moisture.You can say that the air is dry.

Answer 4

That means it will be fairly dry. The humidity percentage has to with the amount of water vapor in the air.

Answer 5

at every temperature point (such as 30*C), there is a max humidity value ( ? g/m3 air). At 30*C, the max humidity value is about 30.29 g/ m3 air. 20% humidity means there are approximately 6 g of vapour per 1 m3 air. The lower the percentage is, the cooler or colder you feel. ( low humidity promote perspiration).

Answer 6

Humidity
Is, a measure of the water vapor content of the air. Popularly, it is used synonymously with relative humidity

http://www.srh.noaa.gov/srh/jetstream/append/glossary_h.htm

so 20% Means that the vapor to air content is 20%

Answer 7

Relative humidity is a term used to describe the quantity of water vapor that exists in a gaseous mixture of air and water.
RH = {p_{(H_2O)} \over p^*_{(H_2O)}} \times 100%

where:

RH_{\,_\,} is the relative humidity of the gas mixture being considered;
{p_{(H_2O)}} is the partial pressure of water vapor in the gas mixture; and
{p^*_{(H_2O)}} is the saturation vapor pressure of water at the temperature of the gas mixture.

Answer 8

It means the air is carrying 20% of the moisture in it that it is possable for air to carry.

Answer 9

it means the air is dry and possibly, rain is not coming.

Answer 10

answers are in this order A, D, E, C, A, B ,E, B