# Electrons in a television set

1. Jan 3, 2008

### krosenberg

A pair of horizontal plates is used to deflect electrons up or down in a television set by placing a potential difference across them. The plates have length 0.04 m. and separation 0.012 m, and the right edge of the plates is 0.50 m from the screen. A potential difference of 200 V is applied across the plates, and the electrons are deflected toward the top of the screen. Assume that the electrons enter horizontally midway between the plates with a separation of 6.0*10^7 m/s and that fringing effects at the edge of the plates and gravity are negligible.

Determine:
1) which of the two plates must be at the higher potential for the electrons to be deflected upward
2) the time required for the electron to move through the plates
3) the vertical displacement of the electron while it is between the plates

I'm totally lost in this problem, but have a feeling we need to find the acceleration of the electron.

2. Jan 3, 2008

### blochwave

Well 1) is simple enough, and you should know offhand that higher potential means more/less charge(you pick the right one!) and opposite for lower potential. In that case, will the electron be attracted towards the side with more or less charge?

2)Don't think "omg a cathode ray tube question wtf"

You've got something traveling right with a known velocity which experiences a force. You can calculate this force cuz you know all the charges and potentials involved and yes, (edit)you can also calculate the acceleration. At that point it's a basic physics 1 problem, use your basic equations and all that

3)If you can do 2 you can do 3

Last edited: Jan 3, 2008