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Electric Fields and Parallel Plates

  1. May 27, 2008 #1
    I just want to know if I'm even given enough information in this question to generate an answer. I don't need an actual answer. Thanks.


    "An electron is fired from a negative plate towards a hole in a positive plate. It then passes between two parallel plates that are 5 cm long and 3 cm apart with a voltage of 750 volts across them. If the accelerating voltage across the two original plates is 1200 volts what is the final velocity of the electron?"

    From the first sentence of the question, it seems like I'm missing the distance between the plates, because with this distance I could calculate the electric field, and consequently continue solving the rest of the problem. Could I calculate it without this distance?
     
  2. jcsd
  3. May 27, 2008 #2

    Doc Al

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    Staff: Mentor

    You are given the voltage between the first two plates. That's all you need.
     
  4. May 27, 2008 #3
    OH! So I should calculate the velocity of the electron as such:

    Delta E = q * Delta V
    (This change in electric potential energy is all converted into kinetic energy.)

    Using the mass of an electron,

    .5 * m * v^2 = q * Delta V
    v = sqrt[q * delta V * 2 / m]

    I'm not sure if that's right.
     
  5. May 27, 2008 #4

    Doc Al

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    Staff: Mentor

    That's the correct way to figure out the speed of the electron as it passes throught the hole. That's the first step.
     
  6. May 27, 2008 #5
    Ah, I think I know where to go on from here. Thanks.
     
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