Why Compact disks have its surface so reflective and colourful? | |
Why Compact disks have its surface so reflective and colourful? And why do we see different colours when we turn the disk around... how to determine the colours reflected with certain angle?
Answers:
1Compact disks are made up of multiple layers of materials.
They have a silver surface to reflect the laser light, so that it can be 'read'. That makes the surface reflective.
On the silver surface, there is a thin layer of plastic on it. The thin layer leads to interference which gives the colours (of the rainbow, the components of white light). This is similar to the colours one sees when oil is spread on water, or for a soap bubble.
The colour depends on the phase difference between the light refelected from the plastic surface and the silver surface. The phase difference depends on the angle at which light is incident on the surface. To determine the colour etc., equations will have to be formed correlating the phase difference and the angle of reflection.
For more details, refer to any good article on 'thin film interference'. One such article is: http://physics.bu.edu/py106/notes/Thinfilm.html
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