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Name: Kim
Status: Educator
Age: 30s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
What is a good junior high science experiment on the topic of dewpoint?


Replies:
Kim,

I'm sorry that it took me a while to respond to your question.

One popular experiment is to take a metal container that is shiny on the outside and place it on something printed or patterned (like newsprint) that can be reflected from the side of the container. Place a thermometer into the container and then mostly fill it with room temperature water. Slowly add ice and slowly stir the mixture; keep doing this until the printing or pattern is not clearly reflected from the outside of the container (dew has formed on the outside of the container). Read the thermometer - the temperature is very close to the dewpoint (it may be just under the dewpoint because of the lag of heat transfer through the container).

You can try this both inside the building and outside (outside if it is above freezing that is) to see the difference in the dewpoint inside and outside. Since there is usually more water vapor in the building (if not air conditioned), the dewpoint temperature should be higher. If the building is air conditioned, the dewpoint temperature outside is usually higher. The dewpoint temperature reflects the absolute amount of water vapor in the air (as opposed to relative humidity, which is temperature dependent).

David R. Cook
Atmospheric Section
Environmental Research Division
Argonne National Laboratory


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