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Inverse Square Law

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    The Exploratorium

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Inverse Square Law

In this math activity related to light, learners explore why a light, such as a candle or a streetlight, looks dimmer the farther away from it we get. The answer lies in the Inverse Square Law, which learners demonstrate using graph paper or perfboard. (Two methods are given for this activity.) Learners will discover that the intensity of light is described by the power distributed over an area.

Quick Guide

Preparation Time:
10 to 30 minutes

Learning Time:
10 to 30 minutes

Estimated Materials Cost:
$5 - $10 per student

Age Range:
Ages 11 - 18

Resource Type:


Materials List (per student)

  • A Mini-Magliteā„¢ flashlight. No substitutes! A point source of light is required for this Snack. (Or make your own economical light source with a square of heavy cardboard, a Mini-Magliteā„¢ replacement bulb, two batteries - either AAA, AA, C, or D - and clip leads to connect them. See Assembly for details.)
  • Graph Paper [Graph Paper Version]
  • Cardboard or foamcore [Graph Paper Version]
  • Perfboard [Perfboard Version]
  • Cardboard to use as a screen [Perfboard Version]
  • A file card
  • A pencil
  • A knife or scissors
  • Ruler
  • Adult help


  • Life Sciences
    • Human Body
      • The Brain and Nervous System
    • Human Senses and Perception
      • Vision
      • Perception
  • Mathematics
    • Algebra
    • Data Analysis and Probability
      • Data Analysis
      • Data Collection
    • Measurement
    • Number and Operations
      • Exponents
    • Problem Solving
  • Physical Sciences
    • Light and Optics
  • The Nature of Science
    • The Scientific Process
      • Conducting Investigations
      • Gathering Data


To use this activity, learners need to:

  • see
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access



  • All Rights Reserved, The Exploratorium,

Funding Sources:

  • National Science Foundation
  • California Department of Education
  • NEC Foundation of America


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