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Max. magnetic force on an electron

  1. Feb 15, 2007 #1
    1. The problem statement, all variables and given/known data
    In a television set, electrons are accelerated from rest through a potential difference of 17 kV. The electrons then pass through a 0.30 T magnetic field that deflects them to the appropriate spot on the screen. Find the magnitude of the maximum magnetic force that an electron can experience.

    2. Relevant equations
    Force = qvBsin(theta)

    B = Force/(charge x velocity)

    3. The attempt at a solution
    Well i am given electrons, i know their mass (m) and charge (q). I am also told that the electron starts from rest (0 m/s) and passes through a potential difference of 17,000 Volts. Then, the electrons pass through a .30 Tesla magnetic field. I don't think i can use equation 1 because i don't know v or sin(theta) and i don't think i can use equation 2 because i don't know the velocity. I would imagine that i need to find a way to tie the potential difference into one of the above equations so i looked at a formula sheet. i just don't see anything that could tie the 2 concepts together. what am i overlooking on this one?
  2. jcsd
  3. Feb 15, 2007 #2


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    Staff: Mentor

    After the electrons are accelerated through the 17kV potential of the electric field, they have a kinetic energy of 17keV. Look up the conversion from keV to Joules, and use that to find their velocity. Then all you need to do is think about how the electron beam and the deflecting magnetic field are oriented in the neck of the CRT, and that will give you your theta value for the maximum deflection force....
  4. Feb 15, 2007 #3
    that definitely makes sense. thank you.
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