Refraction of Light Experiments

Refraction of light is when light bends as it passes at a slant through an interface between two materials. It is a phenomenon familiar to fishermen, who see their fishing lines appear to bend in the water. Several experiments can be used to demonstrate refraction, including using a prism to separate light into the colors of the rainbow.

Bowl of Water

Place a coin at the bottom of a bowl. Step back until the coin just stops being visible over the lip of the bowl. Then have someone pour water into the bowl. Eventually you will be able to see the coin, due to the bending of the light as the coin's image passes obliquely (at a slant) through the air-water surface.

Pencil

Insert a pencil at an angle into a glass tank of water. From above, the pencil seems to bend because refraction has occurred between the water-air interface. But when you look at the pencil from the side of the tank, it appears straight because the light is passing through a flat glass surface.

From the side, you can also look upward through the water surface. Then the pencil will appear bent, because the light from the part of the pencil above water has passed obliquely through the air-water surface.

Jar of Water

Here is an experiment that can show a ray of light bending from refraction. This should be done with the lights out, to see the ray. Place a jar of water in a shoebox. Shine a flashlight through a vertical slit cut in the side of the box. Position the jar so that the light enters the jar obliquely. The ray will then refract twice, once when it enters the jar, and once when it leaves it. The point of the water in the jar is so that the path of light is more visible.

The jar can even be adjusted so that the refraction upon exiting the jar exactly undoes the bending done by the refraction when the light entered the jar.

Prism and Spectrum

As a separate experiment, the jar of water can be replaced with a prism. Shining a ray of light on it can demonstrate Isaac Newton's famous experiment of splitting white light into the colors of the rainbow. To give the colors time to spread out, a different setup than a shoebox is preferred. For example, the light source can be placed in the shoebox, shining out through the slit. The prism would be positioned to catch the light. Then a sheet of cardboard or a wall can serve as the projection screen for the colors.

Spectrum Production

In the experiments above, the prism and the jar both have a point of entry and a point of exit for the light ray. Yet, in the prism experiment, a rainbow spectrum was produced, but in the jar experiment, it wasn't. The colors are separated by passing through the water, but a prism exacerbates the phenomenon by refracting the light twice. Also, the distance from the prism to a wall of projection some distance away allows the colors of the spectrum to spread out. The jar allows spreading only within the confines of the jar, especially if the jar's angle of the point of entry and exit match well.

References

• Kids' Science Experiments - Light