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Electrical Force Problem

  1. Apr 8, 2016 #1
    1. The problem statement, all variables and given/known data
    An alpha particle (charge equals +2e) is sent at high speed toward a gold nucleus (charge equals +79e). What is the electrical force acting on the alpha particle when it is (2.0 x 10-14) m from the gold nucleus?

    2. Relevant equations
    I tried using Coulomb's law, which is E = k(q1q2/r2), with k = 9 x 109.

    3. The attempt at a solution
    I attempted to use Coulomb's law, and plugged it in to get

    E = (9 x 109)(2e)(79e)/(2 x 10-14)

    and my answer was

    E= 2.6 x 1040
    E is a repelling force

    The answer in my textbook is E=91 N and it is a repelling force (I got that part right at least!), and I would really like to know where I went wrong. I was thinking maybe by some chance I plugged it into my calculator wrong, but if someone could double check or tell me where I went wrong, that would be amazing.

    Thank you so much in advance.
  2. jcsd
  3. Apr 8, 2016 #2


    User Avatar

    Staff: Mentor

    In your equation e represents the fundamental unit of charge, not e the base of the natural logarithms. What's the charge on a proton?
  4. Apr 8, 2016 #3
    OH! Thank you so much. I got the right answer. A proton is q = +1.6 x 10-19 C. Now I know that for in the future.
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