Simple Light Refraction Experiment

Light refraction is the bending of light when it hits a substance of a different density.  We’ll show you a simple light refraction experiment you can do at home to demonstrate this quality of light.

When light passes from air to water it is refracted in the water because the water is more dense than the air.  The change in density means the light slows down and slowing down makes it change direction.  When the light changes direction it makes objects in water appear to be in a different place than they actually are.  If you ever dove after a ring in the bottom of a pool you’ve observed this.

This diagram shows what happens to the direction of the light as it passes from one medium to another. The direction change happens because the speed the light travels at changes. Image by Klaus-Dieter Keller, CC license, Wikimedia.

Light Refraction Experiment

All you need is a bowl, with opaque (not see through) sides, a coin, and water.

1. Place the coin in the bottom of the bowl.
2. Back up until you’re about two feet from the bowl, then bend your knees and squat down until the coin is just out of sight under the rim of the bowl.
3. Have a partner slowly pour water into the bowl until it’s full nearly to the rim.

The bowl on the left has a quarter in the middle of it. The camera took the picture from an angle just below where the coin was visible. Without moving the camera the second picture, on the right, was taken after pouring water into the bowl.

The coin will have appeared in your line of sight as the water was poured in.  You can see it because when the light hits the water it slows down and slowing down makes it bend.