1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    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


    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook