A light gets ‘dimmer’ as you walk away from the source of light. This is a qualitative observation (which is obvious to everyone). But how do we describe this mathematically? What quantitative statement can we make? What equation can we use?
Our quantitative statement is the inverse square law. It describes how the intensity of light (or any electromagnetic wave) decreases with distance from the source. It is recommended that students are familiar with the previous post on ‘proportionality’.
These slides have been expanded to offer further explanation.