magnet on TV screen

[luc]

My daughter put a strong magnet near our TV this morning, and obviously this totally messed up the colour on our screen. Thought i would have to buy another, but when i switched it on this evening, after it had been off about 7 hrs, it is fine again

How can this happen? and will there be any long term affects? 

[Gandy]

A tv works by shooting electrons at the screen. The image is actually controlled by magnets pulling the electron beam this way and that. When another magent is introduced, in this case by your daughter it upsets the flow. Once power has been turned of and things are started from scratch again everything will be fine

[smorodina]

The scanning of the electron beams is controlled by electromagnetic coils near the neck of the tube. In order for them to register the correct colour on the tube face they must pass through a shadow mask and hit the correct colour phosphor on the screen. Any magnetism on this metal mask will deflect the beam and cause the wrong colour to be hit.

In order to ensure that any temporary magnetism on the mask is eliminated, there is a 'degaussing' circuit in the power supply that operates, and demagnetises the tube, every time the tv is switched on. There should be no long term effects.

[luc]

Thank you, magnet is now put away in a very high cupboard! 

[romko]

Note that the degauus circuit only operates however if the set is powered on from "cold" - ie.e not from standby. use the mains or wall socket switch.