Sling Psychrometer

ISN

LinkWhat does the word “sling” mean?

Essential Question

• How do you use a sling psychrometer?

?

What’s it for?• Measures the relative humidity (amount of

water vapor in the air)

How does it work?• The dry bulb measures the room temperature.

• The wet bulb has some of the water evaporate off. This cools the bulb making its reading lower than the dry bulb.

• Depending on how much water vapor the air already has, the difference between the dry and wet bulb can be big or small.

How do I use it?1. Find the dry bulb reading.2. Find the wet bulb reading.3. Subtract the wet bulb from the dry bulb.

(Difference)4. Use the chart to calculate the relative

humidity.

The Chart

Practice1. Write down the following table.

Trial # Dry Bulb Wet Bulb Difference b/w Humidity12345678910

Trial #1

Dry Bulb Wet Bulb

Trial #2

Dry Bulb Wet Bulb

Trial #3

Dry Bulb Wet Bulb

Trial #4

Dry Bulb Wet Bulb

Trial #5

Dry Bulb Wet Bulb

Trial # 6

Dry Bulb Wet Bulb

Trial # 7

Dry Bulb Wet Bulb

Trial # 8

Dry Bulb Wet Bulb

Trial # 9

Dry Bulb Wet Bulb

Trial # 10

Dry Bulb Wet Bulb

What do you notice about the relationship between the readings and the humidity?

The smaller the difference the higher the humidity.

• The difference between what this box has inside and what it can hold is small. This means that it’s already pretty full.

• The difference between what this box has inside and what it can hold is large. This means that it’s pretty much empty to begin with.

Warmer air holds more water vapor.

• This is why it’s “sticky” during the summer. • This is why we need lotion more during the

winter because the air is drier and we need more moisture.