Name _______________________________ Period _____ Date ____________
Group Members ___________________________________________________
Objective:
To find out the relative humidity in our classroom, as well as outdoors.
Materials:
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1 thermometer
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2 pieces of gauze

1 rubber band
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small cup of water

piece of paper (optional)

relative humidity chart
Procedure/Analysis:
1. Mea sure the room’s temperature. What is it? (Don’t forget your units!)
Temp in °C: ____ (Temp in °F: ____)
2. Use your hand or a piece of paper to fan the thermometer for 1½-2 minutes.
Did the temperature change? ______________________________________
3. Wrap the piece of gauze around the bulb part of the thermometer, and tie it on with a rubber band.
4. Dip the gauze end into the cup of water. Squeeze out the excess water.
5. Use your hand or a piece of paper to fan the thermometer again for 1½-2 minutes.
6. What is the new thermometer reading?
Temp in °C: ____ (Temp in °F: ___)
7. Subtract the differences between #1 and #6. (°C only!) What is the difference? _____________________________________ (Show your work!)
8. Now look at the relative humidity chart that your teacher gave you. Follow the numbers on the top and side of the sheet…what is the relative humidity in the room right now? ________________________________________________
9. If the air was holding all of the water that it could, what do you think would be the ro om’s relative humidity right now? ______________________________
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10.
Go outside and measure the air’s temperature.
Temp in °C: ____ (Temp in °F: ____)
11. Wrap a dry piece of gauze around the bulb part of the thermometer, and tie it on with a rubber band.
12. Dip the gauze end into the cup of water. Squeeze out the excess water.
13. Use your hand or a piece of paper to fan the thermometer again for 1½-2 minutes.
14. What is the new thermometer reading? Temp in °C: ____ (Temp in °F: ___)
15. Subtract the differences between #10 and #14. (°C only!) What is the difference?____________________________________ (Show your work!)
16. Now look at the relative humidity chart that your teacher gave you. Follow the numbers on the top and side of the sheet…what is the relative humidity outside right now? ______________________________________________

Name _______________________________ Period _____ Date ____________
Group Members ___________________________________________________
Conclusion
1. Do you think that the amount of water in the air affects the rate at which water will evaporate? Explain your answer. (Hint: Think of a wet towel in a damp basement.)
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2. Do you think that the room’s temperature affects the rate at which water will evaporate? Explain your answer. (Hint: Do clothes on the line dry better on a hot day or a cool day?)
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3. What was the difference between the relative humidity indoors and outdoors?
Explain why you think this might be.
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4. How does the evaporation of water cool the wet-bulb thermometer?
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Critical Thinking – Bonus!!
5. Sometimes people say phrases such as, “It’s the humidity that makes us feel so hot, not the heat.” Why do we feel warmer when the humidity is higher?
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Name _______________________________ Period _____ Date ____________
Group Members ___________________________________________________
ANSWER KEY
Conclusion
1. Do you think that the amount of water in the air affects the rate at which water will evaporate? Explain your answer. (Hint: Think of a wet towel in a damp basement.)
Yes, the amount of water in the air affects the rate at which water will evaporate. When water evaporates it fills in the spaces between air particles. The more water that is in the air, the less room there is between molecules to add additional water, and so the harder it is for water to evaporate.
2. Do you think that the room’s temperature affects the rate at which water will evaporate? Explain your answer. (Hint: Do clothes on the line dry better on a hot day or a cool day?)
Yes, the room
’s temperature affects the rate at which water will evaporate.
When the temperature is warm, the air molecules are spread further apart, which leaves more room for water molecules to get in between. At cooler temperatures there is not as much space between molecules and so the water cannot evaporate as quickly. (This is why the air is so dry during the winter months!)
3. What was the difference between the relative humidity indoors and outdoors?
Explain why you think this might be.
___answers will vary________________________________________________
________________________________________________________________
4. How does the evaporation of water cool the wet-bulb thermometer?
In order for water to evaporate it must gain energy. That energy is in the form of heat. The water molecule will take the heat from whatever it is in contact with, in this case, the thermometer!
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Critical Thinking – Bonus!!
5. Sometimes people say phrases such as, “It’s the humidity that makes us feel so hot, not the heat.” Why do we feel warmer when the humidity is higher?
_We feel warmer when the humidity is high because it is more difficult for water to evaporate – this includes the water in our sweat! We sweat as a way to cool our bodies down – the sweat evaporates and takes some of our body heat.
If the humidity is too high, our sweat isn
’t able to evaporate and so we don’t feel as cool.