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MIT Physics Demo -- Magnetic Deflection of a TV Image

An cathode ray tube (CRT) television is connected to a video camera. When a strong magnet is brought close to the television screen, the image becomes warped and discolored.

While many new televisions use flat screen technology, older CRTs produced images by firing electron guns (one red, one green, one blue) through the television body onto the back of the screen. When a magnet is brought close to the screen, it deflects the paths of the electron beams and distorts the picture. A strong enough magnetic field can even create a hole in the electron beams, causing a black spot on the picture.

This TV has been subject to many magnet encounters, which has permanently damaged the picture.

Comments (4)

I did this 12 years ago

Posted almost 6 years by Anonymous User

The process of eliminating magnetization on a CRT is called degaussing (the unit of measure of magnetic inductive force is the gauss, named for mathematician Karl Friedrich Gauss). Most modern CRTs today include built-in degaussing circuits. Some have a manual switch to activate the circuit, some do it automatically and some offer both as an option. The degaussing circuit uses a coil of wire to neutralize magnetic fields within the CRT.

Posted almost 6 years by Anonymous

Hello,
Can you please help me with a question: a month ago a friend of mine accidentally held a tip of a pretty strong magnetised screwdriver very close to my lg flatron 775ft, a crt monitor, while demonstrating something. There were magnetic distortions on the screen around the tip of the screwdriver. He waved with the screwdriver near the monitor surface for about 20-30 seconds until holding it back. Is it possible that this kind of event left permanent damage to the monitor? In terms of picture clarity and refresh rate? Perhaps it is only my autosuggestion, but it feels as if the image is a bit ‘blurrier’ now and more stessful for my eyes (as if i am looking at a screen with lower refresh rate, like below 70Hz, when it is 85Hz). Thanks for answering

Posted over 3 years by gordan

I remember getting in trouble for doing this to our TV when I was a kid!

Posted 1 year by Anonymous 00:01:27

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MIT Department of Physics Technical Services Group

MIT Department of Physics Technical Services Group

Category: Science | Updated over 1 year ago

Created
July 11, 2008 16:51
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