April, 2002, Biology Experiment:

Terrarium Humidity

- Purpose
- Background Information
- Equipment
- Software Set-up
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions



Humidity/Temp/
Dew Point Sensor (PS-2124)

Purpose:

In this experiment, we will use the Humidity/Temp/Dew Point Sensor to measure air temperature, dew point and relative humidity in a plant terrarium. 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.

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. The point at which saturation occurs is called the dew point.

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.

For example, the average relative humidity in the rainforest is high, typically ranging from 75% to 95%.

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Equipment:

For each lab group:

Software Setup:

  1. Click on one of the links below to download a pre-configured DataStudio file for this experiment, and then open the file.

    PASPORT users: Windows (.zip file) or Macintosh (.sit file)

    ScienceWorkshop 500 users: Windows (.zip file) or Macintosh (.sit file)

    When the file is opened, you should see a graph display of Relative Humidity vs. Time, as well as another graph of Temperature vs. Time.

  2. Connect the Humidity Sensor to an Xplorer or USB link (PASPORT users), or plug the two sensors (Humidity and Temperature) into the 500 Interface (ScienceWorkshop 500 users).
    If you are using the ScienceWorkshop 500 Interface, be sure the sensors are associated correctly in the Experiment Setup window when you open the DataStudio file.

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Experimental Procedure:

Data Recording:

  1. Place the Humidity Sensor (and the Temperature Sensor if you are a ScienceWorkshop user) into the terrarium. Leave the terrarium uncovered.

  2. Click the Start button ( ) to begin collecting data.

  3. After 2-3 minutes, place the cover or lid over the terrarium.

  4. After 2-3 minutes, place a cup of hot water into the terrarium. Replace cover or lid.

  5. Continue to record data for 10 minutes.

  6. Click the Stop button ( ) to stop collecting data.

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Data Analysis:

  1. Examine the graph display to view your data, using the Scale to Fit button ( ) in the Graph toolbar to resize the axes if necessary.

  2. Use the Axis Lock button ( ) if the X-axis of the graphs don’t align.

Conclusions and Extensions:

  1. Compare the graph of Temperature vs. Time with the graph of Relative Humidity vs. Time. (Note to PASPORT users: 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?

  2. What factors may have caused the results?

  3. What effect did adding the hot water to the humidity and temperature measurements? Why?

  4. What unique characteristics of the rainforest contribute to the high levels of humidity seen there?

  5. How does the humidity profile of the rainforest compare to seasonal conditions in your hometown?

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