|MadSci Network: Other|
A TV "picture tube" and a computer display screen are both "cathode ray tubes" or CRT's. Dear Pam, The display surface of the tube is coated with a phosphoresecent material, similar to that used in "glow in the dark" stickers or paints. At the back end of the CRT a beam of electrons is shot towards the front. These electrons make the front of the tube glow everywhere they strike it. These electrons can be steered with magnetic fields created by electromagnets. In fact, that is what is being done by the "bump" in the back of your TV. The electromagnets sweep the beam back and forth and up and down to cover the entire front surface of the TV. If you put a very strong magnet at the front of the TV, this field will also steer the beam. The typical effect is that the picture is distorted. You can "magnetize" part of the picture tube in the same way that you can use a magnet to "magnetize" a nail or a screw driver. So you can mess up a TV, but it requires a pretty strong magnet. You can experiment with a refrigerator magnet to mess the picture up a little bit to see how it works. This shouldn't hurt the TV. If it does, tell your mom that your brother did it. When computer displays show the same image over and over again, they can magnetize themselves. This will cause the image to be distorted, sometimes messing up the colors. For this reason, most computer displays come with a feature called "de-gaussing". De-gaussing applies a very strong, quickly changing magnetic field to "scramble" any magnetized parts of the screen. This degaussing will also scramble cassette tapes and floppy discs. Chris Seaman Alcoa Technical Center
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