# Light intensity and the inverse square law

I can explain why light intensity decreases further from a light source.

# Light intensity and the inverse square law

I can explain why light intensity decreases further from a light source.

## Lesson details

### Key learning points

- Light waves spread out as they travel from a light source.
- Further away from the light source, the same amount of light is spread out over a greater area.
- This means the light intensity decreases with increasing distance from a light source.
- Light intensity is inversely proportional to the square of the distance from a light source (inverse square law).

### Common misconception

Many pupils will believe that by halving the distance from a light source, the light intensity will double.

As a result of light travelling in all directions, this aspect needs to be thought of in terms of area (two dimensions). The lesson takes pupils through an example which demonstrates how light intensity is proportional to the square of the distance.

### Keywords

Light intensity - the amount of light reaching a given surface area in a period of time

Light source - an object that emits light

Light waves - oscillations/ripples in electric and magnetic fields

Inversely proportional - variables are inversely proportional when one increases and the other decreases at the same (proportional) rate, e.g. as one variable doubles, the other variable halves

Inverse square law - light intensity is inversely proportional to the square of the distance from the light source

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Video

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