# Water vapour, dew point and humidity

Why do clothes get dry in a tumble dryer?
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Slide 1: Open question
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This lesson contains 20 slides, with interactive quizzes and text slides.

## Items in this lesson

Why do clothes get dry in a tumble dryer?

#### Slide 1 -Open question

Why is it more likely to see dew in the morning after a warm day followed by a cold night?

#### Slide 2 -Open question

Why can you dry your hair with a blow dryer

#### Slide 3 -Open question

Dew point
Air can contain a certain amount of water.

The warmer the air the more water it can contain.

#### Slide 4 -Slide

The dew point tells us how much water vapour 1 cubed meter of air can contain at a certain temperature.

When there is more water vapour than it can contain, the rest will condensate.

When temperature lowers, the amount of water vapour that the air can contain is less. So the water vapour will condensate.

#### Slide 5 -Slide

This graph is figure 29 on page 113.
How much water can 1 cubed meter of air contain at a temperature of 20 C ?
A
22 g
B
20 g
C
10 g
D
17 g

#### Slide 6 -Quiz

This graph is figure 29 on page 113.
What is the temperature if the maximamum amount of water per m^3 is 40 g
A
37 C
B
32 C
C
40 C
D
48 C

#### Slide 7 -Quiz

At the end of a warm summerday it is 24  C. The air contains 16 g per m^3. Could this air hold even more water vapour?

#### Slide 8 -Open question

During the course of the night and the evening the temperature decreases. At what temperature will the water in the air start to condense?

#### Slide 9 -Slide

During the course of the night and the evening the temperature decreases. At what temperature will the water in the air start to condense?
A
10 C
B
18 C
C
0 C
D
24 C

#### Slide 10 -Quiz

Look at 16 g. What temperature goes with it?

#### Slide 11 -Slide

The temperature falls, finally reaching 8 C.
How many grams of water vapour will condense for each cubic meter of air?

#### Slide 12 -Slide

The temperature falls, finally reaching 8 C.
How many grams of water vapour will condense for each cubic meter of air?
A
7 g
B
16 g
C
9 g
D
5 g

#### Slide 13 -Quiz

Look at 8 C. You can see that the air can contain about 9g of water vapour per cubed meter.
There was 16 g in the air and 9 gram will be left, so
16 - 9 = 7 g will condense.

#### Slide 14 -Slide

During a warm day you may sweat.
Your sweat evaporates and that causes you to cool.

But some days you sweat a lot, but still don't cool.

We say then that the weather is sticky or muddy.

It has to do with the humidity of the air.

#### Slide 15 -Slide

The humidity of air is a percentage.

It is calculated by the division of the content of water vapour in the air divided by the maximum content times 100%

#### Slide 16 -Slide

Example:
The maximum amount of water vapour at 33 C is 34 g.

At a hot summer's day it is 33 C and the air contains 12 g of water vapour?

Calculate the humidity.

#### Slide 17 -Slide

Data: maximum amount  = 34 g
amount in air = 12 g
required: humidity
workings:

h=(maxamount)(amount)100
h=3412100=35
Tekst

#### Slide 18 -Slide

At a certain day the maximum amount of water vapour that the air can hold is 24 grams. The air contains 20 grams. Calculate the humidity.
A
84%
B
120%
C
83%
D
20%

#### Slide 19 -Quiz

Summary

The dew point is the point where water starts to condense. The aireither contains too much water vapour or the temperature drops.

humidity is the ratio between the amount of water vapour the air contains and the maximum amount.