HOW DO YOU BEND LIGHT?

A. Materials needed:

1. A transparent glass
2. A pen
3. Plane paper
4. Clean water

B. Instructions:

1. Draw a tiny arrow on the plane paper pointing left or right.

2. Hold the paper upright against the glass so that you can clearly see the arrow through the glass from the opposite end of the glass.
3. Slowly pour some clean water into the class until it is filled to the brim.

4. Observe your arrow enlarge and change direction!

SO HOW DOES THE ARROW ENLARGE AND CHANGE DIRECTION?

When light travels into a different medium (say from air to water) it tends to bend towards the normal. The normal is a line imagined perpendicular to the [horizontal] surface  of the second medium.

The extent of bending depends on the refractive index of the medium. The higher the refractive index, the more the medium is able to reduce the speed of light and the more a light ray passing through it bends towards the normal. In this experiment, the light from the arrow passes through three media before reaching the eye: Water to glass and then air; bending at each of these media. This creates the perception of changed direction as observed. The image is perceived enlarged because the results of these bendings bring the exiting light ray closer to the eye.

The same phenomenon can be observed when a glass bottle filled with water is placed atop a coin. The coin seems to dissapper. This is because light from the coin gets defracted by the water and does not reach the eye, thus we are unable to see the coin.

TAKING IT FURTHER

Repeat this experiment with a different liquid. Do you get the same results? Explain your observation. Have fun observing changes to different drawings!