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Educational field courses for educators & students in
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Cut the Humidity with a Knife
Purpose:
In this experiment, we will use the Relative Humidity Sensor to measure air temperature,
dew point and relative humidity over a 24-hour period. We’ll then hypothesize reasons for any changes.
Background Information:
The amount of water vapor in the air is called humidity. As water molecules evaporate, the humidity of
the air increases. Certain climate regions on earth (such as deserts, Arctic and Antarctic regions) have very
low humidity, while other climate regions (such as tropical rain forests) have moderate to high humidity.
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In general, the amount of water vapor that a given volume of air can hold increases as the temperature increases.
A higher temperature allows more water to evaporate into water vapor. As the temperature goes down, the amount of
water vapor in the air goes down because the water vapor molecules can condense into liquid form again.
Therefore, the humidity drops. When the air holds all the water vapor it can at a given temperature, the air is
saturated.
Relative humidity is a common way to describe the amount of water vapor in the air. Relative humidity is a ratio that compares the mass of water vapor in the air to the mass of water vapor that the air can hold at its saturation point. Relative humidity is always written as a percentage.
The average relative humidity in the rainforest is high, typically ranging from 75% to 95%.
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Equipment:
Equipment Set-Up:
- Connect the USB Link to your computer's USB port.
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Connect the Humidity sensor to the USB Link.
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Data Collection Procedure:
1. If DataStudio is not already running, it will launch once the USB Link is connected to the computer.
2. Click on the “Launch DataStudio” icon in the PASPortal window.
3. We’ll record data over a 24-hour period and set our sample rate, once every 5 minutes.
a. Click the Setup button (
).
b. The "Sample Period" default will read "5 Hz". Change it to "5 Minutes" by using the pull-down tab.
c. Click (
) to close the "Experimental Setup" window.
4. Click the Start button (
) to begin collecting data.
5. Click the Stop button (
) after 24 hours to stop collecting data.
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Data Analysis:
1. Scale the axes to fit the data using the Scale to Fit button (
) in the Graph toolbar.
2. Examine the graph and study the data.
3. Enter annotations noting approximate sunrise/sunset times, any change in visible weather patterns (i.e. rainstorm, clouds, wind…).
a. Click the Annotate button (
), and enter your text.
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Conclusions and Extensions:
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- Compare the graph of Temperature vs. Time with the graph of Relative Humidity vs. Time. (Note: since this is a multi-sensor, you can also compare these graphs with a graph of Absolute Humidity vs. Time.) How does a change in temperature affect relative humidity?
- Did changes in relative humidity coincide with any changes noted in weather patterns?
- Is relative humidity generally higher during the day or night? Why?
- What unique characteristics of the rainforest contribute to high levels of humidity? How does the humidity profile of the rainforest compare to seasonal conditions in your hometown?
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| This experiment is brought to you courtesy of
PASCO. |
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Equipment
