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Homework Help: Potentia Difference and Electric Potential

  1. Feb 24, 2009 #1
    A proton moves 2.00 cm parallel to a uniform electric field of E = 200 N/C. (a) How much work is done on the proton by the field? (b)What change occurs in the potential energy of the proton? (c) What potential difference did the proton move through?

    I really just need help with Part A, I should be able to get through the rest alright. I'm not entirely sure what the charge of the proton would be. I know that wok is equal to the change in potential energy, which is then equal to (kq1q2)/r.....but I'm not sure what the chrages would be. Help?
  2. jcsd
  3. Feb 24, 2009 #2


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    The charge on the proton is the same as the charge on the electron (except it is positive), often called the "elementary charge". You can easily look up its value in your text or in Wikipedia.

    V = (kq1q2)/r applies only two point charges. For this problem with the uniform E field, you really need F = qE, an electric field causes a force on a charge. From there you can find the work done quite easily.

    In a uniform E field, E = V/d. This is often called the parallel plate formula because it tells how a potential across plates distance d apart causes a uniform electric field between the plates. You could use it backwards to find your part c.

    Alternatively, use the definition of potential difference = (change in energy)/charge.
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