Brightness and Distance:

The Inverse Square Law

Summary:

The inverse square law is a relationship between the brightness of a light and distance from the light.

Materials:

• Light meter
• Table lamp
• Meter stick
• Graph paper
• Worksheet
• Calculator

Before you start...

1. Read the safety notes for this experiment.
2. The questions in green below should be answered on your worksheet!
3. The questions in bold below should be answered on your worksheet!

Procedure:

1. Take out your worksheet.
2. Read the background material for this section.
3. Summarize the background material in three short sentences.
4. Turn on your table lamp. It represents a star in this experiment!
5. Move your light meter until it reads 2000. Record the distance between the light and the light meter on your data table. (an example of the data table is here).
6. Continue filling in your data table. One column should be the light meter reading and the other should be distance from the light bulb. The light meter readings are already filled in for you.
7. Graph your data, with distance in centimeters along the horizontal axis, and the meter reading along the vertical.
8. Read the disscussion of the inverse square law.
9. Calculate the inverse square law predictions for the distances you measured; the table on your worksheet explains how to do this.
10. Add these predicted data points to your graph. You might want to use a different color pen for the predictions so that you can keep them separate from the distances you measured!
11. How do these predicted distances compare with the ones you measured? List at least 3 possible reasons for any differences.

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    Matt Craig
    Last modified: Tue Jun 1 16:03:26 PDT 1999