Why Compact disks have its surface so reflective and colourful?

Question

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?

Answer 1

Compact 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

Answer 2

Cd's are so colorful because the laser that is directed onto the surface of the CD must be reflected back to a light detector. Even though the surface of the disk appears flat there are slight variations in the surface. The slight variations cause white light to reflect at different angles that is why if you hold a cd near a white light source you see a rainbow type effect. But in acutal operation only one color of light from a laser is directed onto the surface.
To understand why light reflects at different angles you may want to do some research on the diffraction of light.

Answer 3

The surface of a compact disk is extremely thin, similar to the thickness of a soap bubble in your bath.
Remember the rainbow colours you see on them?
It is the same with the CD. Visible light ranges from red to violet, that is a range of wavelengths. When the wavelength of a given colour is the same as the thickness of the CD film, it is reflected to you, so you see the rainbow of colours.
To determine what would be the colour reflected for a given angle, you will have to calculate the length of travel through the film in "oblique" (and also know the thickness of the film, and the wavelengths of each colour, and the angles, and your trigonometry formulas!)

Answer 4

The "information" on a CD or DVD is impressed onto the plastic disk when it is molded. (small impressions in the plastic which correspond to the 1's and 0's which the laser will "read" as digital information) The plastic doesn't reflct much light until it is metalized - coated with a very thin layer of shiny silver or gold. This surface is very fragile and it is followed by a coating of laquer to protect it. This clear coating on the surface "bends" the light (first entering the disk and again when it exits) and the reflctive metal sends the defracted light back, much the same as when you "create" a rainbow by misting the water from a garden hose on a bright, sunny day.

Answer 5

iT HAS to reflect all frequencies of light. this means that it has to reflect all colors of light. THIS IS BECAUSE WHEN IT IS READ BY THE LASER IN CD-ROM's, THE LIGHT THE LASER EMITS SHOULD NOT BE ABSORBED. if a frequency of light is not absorbed, it is reflected... BLACK ABSORBS ALL COLORS OF LIGHT... THE COLOR WE SEE FROM AN OBJECT IS THE ONLY COLOR IT REFELCTs, ALL OTHER COLORS WE DO NOT SEE FROM THE OBJECT IS ABSORBED BY THE OBJECT.

we see a green leaf because leaves reflect only GREEN LIGHT... all other frequencies are absorbed by the leaf.

THE cd reflects all COLORS OF LIGHT at different parts of it...

Answer 6

to be light friendly