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Speed of an Electron in an Electric Field

  1. Apr 17, 2008 #1
    1. The problem statement, all variables and given/known data

    Two stationary positive point charges, charge 1 of magnitude 3.25 nC and charge 2 of magnitude 1.55nC , are separated by a distance of 57.0cm . An electron is released from rest at the point midway between the two charges, and it moves along the line connecting the two charges.

    find Vfinal of the electron when it is 10.0 cm from charge 1 the want the final answer in m/s

    i dont get any of this my professor went to fast. can anyone help?
  2. jcsd
  3. Apr 17, 2008 #2


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    This looks like a conservation-of-energy problem.

    The two relevant forms of energy are kinetic and electric potential.
  4. Apr 17, 2008 #3
    do you know of any equations that could help me
  5. Apr 17, 2008 #4


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    Your book or class notes will have an equation for the electric potential (or voltage) due to a point charge.

    To get the net electric potential of the two stationary charges, add up the individual potentials of each of the two charges.

    To get the potential energy, multiply electric potential times the charge on the electron. Watch the +/- signs carefully.
  6. Apr 18, 2008 #5
    can any one help me
  7. Apr 19, 2008 #6
    q1 = 3.25 nC, q2 = 1.55nC, d = 0.570 m. charge of electron = q, a = 0.100 m, find the final speed of the electron, v = ?
    initial kinetic energy Eki = 0, potential energy Epi = Kqq1/(d/2) + Kqq2/(d/2)
    final kinetic energy Ekf = mv^2/2, potential energy Epf = Kqq1/a + Kqq2/(d-a)
    energy conservation:
    0 + Kqq1/(d/2) + Kqq2/(d/2) = mv^2/2 + Kqq1/a + Kqq2/(d-a)
    solve for v.
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