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Homework Help: Speed of Impact of electrons in a television.

  1. Feb 19, 2009 #1
    1. The problem statement, all variables and given/known data

    What is the speed of impact of electrons with the screen of the picture tube? Answer in units of m/s.

    Electrons are accelerated through a potential difference of 15500 V
    Charge of electron: 1.6 x 10^-19 C
    Mass of electron: 9.11 x 10^-31 kg
    Energy of electrons when they hit the screen: 2.48E-15 J

    2. Relevant equations

    v=Ed
    f=ma
    f=qE
    K = .5mv^2

    3. The attempt at a solution

    I tried using that equation, I made it 15500 = .5mv^2 ... obviously plugging in the above numbers for m and v.

    Computer said the answer was wrong.
     
  2. jcsd
  3. Feb 19, 2009 #2

    Delphi51

    User Avatar
    Homework Helper

    Goodness they calculated the electron energy for you! Too easy!

    So just use 2.48E-15 J = 1/2mv^2

    Potential is the energy per charge, so you could start with V = E/q, and replace E with 1/2mv^2.
     
  4. Feb 19, 2009 #3
    No, I calculated that for a previous problem...

    Thanks though, got it right now.
     
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