What actually is a CD?
Before we go into the process of how a CD player works, we first need to know what it actually is. A CD isn't just a shiny, plastic disc, it is essentially made up of 3 different layers. Most CD's are made in the same way. Normally they have a tough plastic layer called the Polycarbonate Plastic Disc, first data is imprinted which creates more 1s and 0s (this is explained further on). The next layer is the reflective foil layer, a micro attenuate of aluminium is exerted to the top of the CD which covers the data, This layer reflects light back through the plastic disc permitting the imprinted data to be read. On the third layer lacquer is put onto the disc ans then spun at a high speed to create a thin layer of sealant for the foil layer. This seals in the foil layer but it gives very little protection for the data beneath. Finally there is the graphic layer, here a layer of ink which usually has a label written on it is screened onto the lacquer layer.
The most important part of a CD is the side which is shiny and reflective because this is where all the information is stored. Previous technology used electromagnets (used in a tape) or mechanical or analogue technology (used in a record). A CD uses optical technology to store information, this requires a laser bouncing off the reflective side onto the CD and back to the photoelectric cell. CD's store information in an unusual but smart way. A particular amount of data is recorded onto the CD. The analogue signal is converted by the 'analogue to digital converter' into a long sequence of numbers, this is called sampling. The sequence of numbers is then stored onto CD in binary form of 1s and 0s, every 0 and 1 is referred to as a bit. These bits contain pieces of information, the complete sequence is called a binary code.
The most important part of a CD is the side which is shiny and reflective because this is where all the information is stored. Previous technology used electromagnets (used in a tape) or mechanical or analogue technology (used in a record). A CD uses optical technology to store information, this requires a laser bouncing off the reflective side onto the CD and back to the photoelectric cell. CD's store information in an unusual but smart way. A particular amount of data is recorded onto the CD. The analogue signal is converted by the 'analogue to digital converter' into a long sequence of numbers, this is called sampling. The sequence of numbers is then stored onto CD in binary form of 1s and 0s, every 0 and 1 is referred to as a bit. These bits contain pieces of information, the complete sequence is called a binary code.
CD to Loudspeaker
Inside a CD player there is a miniature laser called the semiconductor diode laser and a small photoelectric cell. When the play button is pressed, an electric motor causes the CD to revolve rapidly. The laser/light beam begins scanning along the track from the center outwards. As the laser and photoelectric cell finish scanning when the track number increases, the motor slows down the speed of the CD. The job of the lens is to direct the laser at particular points on the disc. The lens is needed because CD's can differ in thickness. The lens has a magnetized pole surrounded by a focusing coil. An electrical current flows through he coil which turns the lens to gain focus. They can also move marginally to each side to make sure that no errors are made when reading the disc. The lens permits the light from the laser beam to be aimed on a specific point on the dis, this also reduces errors, this is done by using the process of refraction. Rays of light from the laser beam start off close together; a focal point on the disc is created by the lens which are convexed shape, this is due to the laws of refraction. Because of the shape of the lens, when light flows through it, the beams are bent towards the focal point where all of the rays of light cross. The position of the lens is controlled to make sure that the focal point is where the aluminium layer of the the CD; therefore the focused beams hit the pits and lands from which the light is reflected.
If you used a microscope on a CD, you would be able to see Pits (bumps) and Lands (flat areas). These different surfaces reflect light dissimilarly , when a light ray hits a land, it reflects the light straight back. at a 90 degree angle. However when the ray of light from the laser beam hits a pit, the light reflects off the disc at many different angles, consequently the light refracts. If the light is successful and reflects back, the photoelectric cell detects it and recognizes it as a land. This transmits an electric current to an electronic circuit producing the number 1. Each time the light fails to reflect back, however, proving that it has hit a pit and dispersed, the photoelectric cell doesn't register anything and the electronic circuit produces the number 0.
If you used a microscope on a CD, you would be able to see Pits (bumps) and Lands (flat areas). These different surfaces reflect light dissimilarly , when a light ray hits a land, it reflects the light straight back. at a 90 degree angle. However when the ray of light from the laser beam hits a pit, the light reflects off the disc at many different angles, consequently the light refracts. If the light is successful and reflects back, the photoelectric cell detects it and recognizes it as a land. This transmits an electric current to an electronic circuit producing the number 1. Each time the light fails to reflect back, however, proving that it has hit a pit and dispersed, the photoelectric cell doesn't register anything and the electronic circuit produces the number 0.