Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 23/04/2008 14:13:15
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how and why does it get there on CRT TV's, and why is it not there on TFT Flat screens?
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Do you mean the electrostatic charge that builds up on a crt or the 'snow' stuff that's displayed upon it?
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how and why does it get there on CRT TV's, and why is it not there on TFT Flat screens?
If you mean the static electricity - it feels charged, you can "stick" a piece of paper to it, and it crackles when you move your hand/finger near it, then...
A CRT fires an electron beam at the screen with a charge of 25kV (for a colour TV - somewhat less for black-and-white). Not so surprisingly this tends to cause the glass to become charged. I don't know much more detail than that.
An LCD screen works at very low voltage, maybe -10/+30V maximum - so you won't get any static electricity. Every pixel on a TFT LCD screen contains a tiny thin-film field-effect transistor ... and these are easily damaged by static electricity - much care goes into the design of the screen and especially the factory that makes them to ensure they don't get exposed to damaging static!
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It's charging by electric induction due to the high energy electrons hitting the other side of the glass. AFAIK there is no actual conduction of electric current through the glass. The energy for the spark you can get from the face of a crt is supplied by the movement of your hand.