DANIEL SAMBRAUS, THOMAS LUDDINGTON / SCIENCE PHOTO LIBRARY DANIEL SAMBRAUS, THOMAS LUDDINGTON / SCIENCE PHOTO LIBRARY
Optical discs. Compact discs (CDs) and digital versatile discs (DVDs) are examples of optical discs. An optical disc digitally stores music and other data as tiny depressions in a plastic disc. This disc is coated with a fine film of metal and then by another layer of plastic. The depressions form a spiral track moving from the centre of the disc to the outer edge. The data track is about 0.5 micrometres wide, and would stretch out for nearly 5 kilometres if unravelled. The information is read by a laser light that reflects from the metal layer, allowing the original data to be reconstructed.
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