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Magnetism Inside a Television

 Gray - phosphorus
screen

Green - magnetic field

Blue - electron

Pink - electron gun

You are looking at the view of a cathode ray tube (CRT) from the inside. The CRT is used in televisions and computer displays (not LCD or Plasmas). This model demonstrates how charges are "shot" onto the back side of a television screen (shown in gray). The electron gun uses high voltage and high temperature to shoot electrons straight toward the screen. Electromagnets around the picture tube (not shown) are capable of creating magnetic fields of different strengths and directions. The moving electrons create a magnetic field of their own which interferes with the larger magnetic field it is passing through. As a result if these two fields trying to occupy the same space at the same time, a magnetic force is created which pushes the moving electron in a different direction. By adjusting the strength and direction of the magnetic field the electron can be made to strike any point on the screen. By adjusting where the electrons strike the screen, a picture can be "painted" on the screen which you can then see from outside the television. In a real television this electron gun fires many thousand electrons per second so this process happens much more rapidly than shown here.

In a Black & White TV it can take as many as 300,000 electrons to make one image. In a color TV it can be 3 times that many. You should also realize that a new picture gets "painted" on the screen 24 times a second. That means in a color TV or computer monitor there are over 23 million electrons fired at the screen per second! That also means the magnetic field created by the TV must also change 23 million times a second. A color TV would actually have three different electron guns. One gun would shoot at the red phosphorus, one at the blue phosphorus, and one at the green phosphorus. Together the three colors can form any color needed to paint that picture. For explanations of how the invisible electrons produce visible light you should look to sections on light and waves.