Compact Discs

Composition of CDs

-Compact discs are made up one quarter (1/25) of an inch of material.

        -A majority of that material is injection-molded piece of clear polycarbonate plastic.

                -Plastic is encoded with microscopic bumps that form one continuous spiral track of data

        -Thin, reflective layer of aluminum placed over bumps on plastic

        -Thin acrylic layer spread over aluminum for protection

                -Label of CD is printed onto acrylic layer

Cross-section of a CD

-The shiny side of the CD is considered the "play side"

How do they work?

-Made up of continuous spiral track of data, which starts on the inside to the outside of the disc       

        -Data track is extremely small (approximately 0.5 microns wide), and typically there is 1.6 microns between the tracks              

(1 micron = 1 millionth of a meter)

                -Bumps that form the track are even smaller

                        -The bumps are elongated, ranging from 0.83 microns to 125 billionths of a meter in length

 Sample of bumps on a CD data track

-A red single-beam laser reads the bumps found on the track

Did you know?

        If you take all of the bumps from the data track of a Compact Disc and stretched them out into a straight line, it would be nearly 3.5 miles long!

                           Homepage                                                                    >> Next Page (CD Players)

This page is not that of a real company but is for a chemistry assignment for General Chemistry 140 at Monmouth College.