Light & Optics: Inverse Square Law

Explore the relationship between the intensity of light and the distance from the light source.

Your students can easily combine hand-collected data with measurements from a light sensor to illustrate their relationship.

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Lab Summary

Students will use a Light Sensor to investigate the inverse square law. Students will measure the intensity of a light source as the distance between the sensor and the light source is increased. They will examine the shape of the graph and determine how the intensity of light is related to the distance.


Light intensity decreases by the square of the distance from the source.  With a small light source and a polarizing filter, the Light Sensor can accurately demonstrate this relationship.



Use a Light Sensor to measure the light intensity from a small light source as the distance of the sensor from the source increases. Examine the graph of light intensity versus distance and versus distance squared to determine the relationship that best fits the data.

Here's What You Need

U.S. Educator prices shown.

Required for computer-based lab: (See lab download for Xplorer GLX-based lab requirements, which may differ)


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PASPORT Light Sensor (PS-2106A) - $59

Features a wide measurable range by offering three light ranges accommodating various different measurement situations. For use with PASPORT Interfaces.

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Xplorer GLX (PS-2002) - $389

The Xplorer GLX is a data collection, graphing, and analysis tool designed for science students and educators.

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Other Products

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Basic Optics System (OS-8515C) - $499

A group of components designed to allow students conduct various optical experiments.

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Aperture Bracket (OS-8534A) - $99

With the Aperture Bracket, a student can vary the spatial resolution of the Light Sensor in six steps from 0.1 to 1.5 mm. Mounts to Basic Optics Bench.

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Lab Manual

The computer-based activity is included in Explorations in Physics (PS-2810). The Xplorer GLX-based lab is included in Physics with the Xplorer GLX (PS-2826). Both manuals are complete with Teacher Information pages, student instructions and handouts, and sample data.

For your convenience, we offer bundles which provide the probeware for the activities in the manual. For more, please see:
Computer-based Physics Lab Manual and Bundles
Xplorer GLX-based Physics Lab Manual and Bundles