Different Colors on a CD

Aim:

To understand the reason behind different colours we see when light reflects off a compact disc.

Materials required:

1.A compact disc which cannot be put to use later.
2.A white paper sheet.

Procedure:

1.Take the compact disc. Look at the side that is not printed under sunlight. We will see bands of different colours shimmering off the disc’s surface and also that the colours shifts as we incline or move the disc sideways.
2.Hold the piece of paper so that the sunlight reflecting off the CD falls on the paper. If there is not enough sunshine then turn off the lights and use a flashlight in place of sunlight.
3.Change the angle of incident light on the CD by tipping it. Also shift the paper so that the distance of the paper from the CD changes. Observe the changes in the colours.
4.Now look at the coating on the CD closely. You will see it has a coating of aluminium with plastic. The colour visible is because of splitting of white light off the aluminium ridges.

Scientific explanation:

The compact disc has thousands of concentric circles on it. These circles are like projections in the disk which results in splitting of light when white light is incident on it. This is because of the reflection off the surface of the aluminium coating which are like projections and this is same as splitting of light by water droplets. With the change of angles of incident light on the CD when it is tilted, the waves tend to add together and form different colours or even cancel each other out. Thus certain colours of the spectrum are formed.