Relative Humidity

What is a psychrometer?

A psychrometer has two thermometers. The dry bulb thermometer measures air temperature. The second thermometer has a wet bulb. As water evaporates from the wet bulb, its temperature decreases relative to the air temperature.

At what dew point temperature will it start to feel humid?

Around 18 degrees Celsius.

How does relative humidity change as air cools down in the evening?

As air cools down in the evening, relative humidity increases because the air can't hold as much water vapor, but is holding a lot already.

How does the amount of water vapor air can hold changes as air temperature increases?

As air temperature increases, the amount of water vapor air can hold increases.

How does relative humidity change as air warms up in the morning?

As air warms up in the morning, relative humidity decreases because it can hold more water vapor than it is already holding.

As the dry bulb temperature increases, what happens to the relative humidity?

It decreases

As the wet bulb depression increases, what happens to the relative humidity?

It increases, since the temperature is increasing. (The wet bulb changes temperatures slower than the dry bulb, so as temperature increases, the dry bulb temperature increases faster. Therefore, the greater the temperature, the greater the wet bulb depression.)

What happens when the dew point temperature is close to the actual temperature?

It will rain.

How do you find relative humidity given a table?

Locate the dry bulb temperature, then locate the wet bulb depression. The intersection of the row and the column is the relative humidity.

Is relative humidity a good way to determine how muggy it is outside?

No, because it is a ratio, not a value. 50% relative humidity at 50 degrees feels way less muggy than 50% relative humidity at 80 degrees.

What instrument is used to measure relative humidity?

Psychrometer

What happens to relative humidity as temperature increases?

Relative humidity decreases in percent. As air warms up, it can hold more water vapor than it is already holding. The volume increases while the moisture in the air stays the same, so the percent of the air occupied with water decreases.

What happens to relative humidity as temperature drops?

Relative humidity increases in percent. Cooler air can hold less water, so it fills up faster.

What does relative humidity depend on?

Temperature

What happens when air cools down?

The air condenses and has a lower volume.

What happens when air warms up?

The air expands and has a greater volume.

What is density?

The amount of mass per unit of volume. The amount of 'stuff' in a given 'space'.

What is mass?

The amount of matter (stuff) the object/substance is made of.

What is volume?

The amount of space an object or substance takes up.

What is wet bulb depression?

The difference between dry bulb and wet bulb temperatures

What is relative humidity?

The percent of water vapor in the air compared to the maximum amount of water vapor the air can hold at the same temperature and pressure. It is a ratio, not a fixed value like dew point.

Why can warm air hold more water vapor than cold air?

Warm air is less dense, and the particles are more spread out.