Technology Idea
Albedo Effect
Probeware Lab

Background:

When solar radiation strikes the Earth, it is either absorbed or reflected. How much is reflected and how much is absorbed depends on the type of surface that the sunlight strikes. Scientists describe the reflectivity of a surface with the term albedo - it is based on the percentage of solar radiation that is reflected.

In this lab, a light sensor will be used to detect the amount of reflected light from various colours and surfaces.

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The Question:

How does the reflectivity of different surfaces compare?

Variables:

Identify the type of data you will collect to support your hypothesis and state the manipulated, responding and controlled variables in this investigation.

SAFETY REMINDER: The lamp will be hot.

Materials:

  • gooseneck lamp with 60 watt bulb
  • light sensor
  • USB link to computer or handheld Xplorer
  • lab stand
  • two clamps
  • several aluminum pie plates
  • coloured construction paper (suggestions: white, green, brown, black)
  • various Earth surfaces (suggestions: dark soil, sand, sod, gravel, snow, water)

Procedure:

Step 1:

Connect the light sensor to your computer - you can use a USB Link connection, or alternatively, you can use a handheld data collection unit instead of a computer and take reflectivity readings directly from the handheld:

Step 2:

If you are using the handheld, you will have to record readings from the handheld display.

If you are using a computer, open the DataStudio software and configure it to display a light intensity graph and digital readout:

Step 3:

Equipment Setup:

  • Clamp the gooseneck lamp to one side of the lab stand about 15 cm up on the stand. Aim the lamp at a slight angle, pointing almost directly straight down.
  • Clamp the light sensor at a slight and opposing angle to the lamp, pointing almost directly straight down. Make sure the sensor is just slightly higher than the lamp (no direct light from the lamp should strike the sensor). The entire setup should be similar to pictured below:

Step 4:

Data collection:

  1. Turn on the lamp, and press the middle sensitivity button on the light sensor.
  2. Place the white piece of paper at the base of the lamp. Have the rest of the colours ready for placement in the same position. Organize a data table for recording reflectivity values for each of the colours.
  3. Place a white sheet of paper at the base of the lab stand. Click the Start button ( ) to begin collecting data.
  4. Allow the data to collect for about 10 seconds - record the light intensity value you see in the digital display in your data table (note that if you are graphing the data, you may have to auto-scale the data to see the difference between paper colours).
  5. After the 10 seconds, place a different colour on top of the white paper, and record the digital readout again, and repeat this process for all of the different colours.
  6. Click the Stop ( ) button, and print out your graph.
  7. Repeat steps 3-6, but this time using aluminum pans filled with the Earth surfaces you have collected.

Analyzing and Interpreting:

1. Which of the colours represented the highest albedo? Why do you think this is so?
2. Which of the Earth surfaces you tested represented the highest albedo? Why do you think this is so?
3. Carefully compare the reflectivity of the colours to the reflectivity of the Earth surfaces. Was there are a correlation between similar colours (soil and brown, snow and white)? Explain why or why not.

Forming Conclusions:

4. Based on the data you have collected, write a summary statement for the following question:

How does the reflectivity of different surfaces compare?

Extending:

5. Surfaces that absorb more radiant energy should incur a greater increase in temperature than surfaces that absorb less. Design an experiment to test this and carry it out.

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