Eli5 What was the static on a CRT TV screen and how did it get there?


I was talking to my brother the other day about what kids these days well never experience and this topic came up.

I remember as a kid I liked to brush my hand on the tv screen so I could feel the fuzzy air. What was that and why was it there?

In: Physics

CRT – Cathode Ray Tube- displays work by directing a beam of electrons into the screen to produce an image. All those electrons will also create an immense static charge in and around the screen, which attracts the hairs on your skin due to their opposite charges.

In order to get a TV signal, you have to send data. Nowadays, that signal is sent digitally via a cable or satellite. In the old days it was sent through the air and picked up by an antenna.

For various different reasons, that signal through the air could get messed up a little bit and you’d miss a tiny part of the picture/sound. That is static. The attempt to translate those small mistakes into a picture/sound.

CRT televisions displayed an image on a screen made out of a phosphor – a material that glows when exposed to radiation. In the case of the TV, the phosphor was designed to glow in response to electron radiation, as this is easily produced and controlled precisely. By changing the strength and direction of a beam of electron radiation (using magnets) an old CRT TV would scan over every pixel on the screen dozens of times every second and draw out the image in the phosphor.

So, you have what’s more or less a constant stream of electrons barraging the inside of the glass screen, and they’ve got to go *somewhere*. They pile up in the glass, producing a negative static charge and seeping out into the surroundings.