Eli5: What happens when you hold a magnet up to an old crt TV?


Eli5: What happens when you hold a magnet up to an old crt TV?

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Depends on where you hold it and how strong it is.

There’s already an electromagnet inside directing the scanning beams.

CRT tvs used electromagnets to move an electron beam across/down the screen. Where the beam hit lit up in a certain colour for each pixel depending on what part of the pixel the beam lands on. The magnet you’re holding adds to the built in magnets and the beam lands in the wrong place activating the wrong colors.

I fucked up the family TV with a magnet when I was a kid. Turning it off and on didn’t help, and I freaked out I was going to get in huge trouble. Fortunately, I found a curious button on the back of the TV labeled “degauss”…

The front panel of a CRT TV is coated with stuff that glows for a bit when hit by electrons. At the back of the TV there’s a hot filament that sends out electrons, and a high voltage that flings them toward the screen.

As charged particles with low mass, electrons can easily be moved by magnetic fields. And electromagnets are magnets that can be precisely controlled. So the electrons can be very precisely aimed at different spots on the screen by electromagnets. The electron beam is [only pointing at one pixel at a time](https://www.youtube.com/watch?v=3BJU2drrtCM), but there’s a circuit that sweeps the aim across the screen to create rows of pixels.

An outside magnet disrupts the aiming of the electrons and distorts the picture.