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Thursday, December 20, 2012

Dewpoint and Relative Humidity Labs

Both of these labs can be done in one day.  For dewpoint, I used glass beakers. I have known teachers to finally have a use for all those glass babyfood jars they saved. One teacher carefully saved cans from canned vegetables she used at home. The metal is very quick to show condensation.

Dewpoint lab

Air temperature _________

Temperature of water _________

Slowly add ice to water.

Temperature of water when you first see dew __________

Temperature of water two minutes after you first see dew ______

Why is dewpoint more accurate when you first see dew?
___Dew is produced at dewpoint and lower temperatures.________

Where does the dew come from?
___The air surrounding the container.____

Humidity lab

Dry bulb reading _________ 
Air temperature.

Wet bulb reading _________
Wet gauze is tied to the base of the thermometer. You can use a sling psychrometer which has two thermometers. One of which has a wet gauze attached.

Difference between the dry bulb and wet bulb reading ______

The greater the difference between the dry bulb reading and the wet bulb reading, the drier the air is. More evaporation occurs because the air is able to hold more moisture. When the air is totally saturated, no more water will evaporate and the dry and wet bulb readings will be the same.

These charts produced by University of Waterloo in Ontario, Canada were the best charts. I liked having students use charts. You will also find calculators and formulas that take into consideration air pressure. These charts give good results. The biggest mistake I see is people using a heat index chart which is a different concept.

Relative humidity __________

The ___________ (greater, less) the temperature difference between the dry bulb reading and the wet bulb reading, the drier the air or lower the relative humidity will be.

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