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Homework Help: Finding the Force of Nucleus on a Single Electron of Plutonium

  1. Jan 30, 2013 #1
    1. The problem statement, all variables and given/known data

    A particular nucleus of the element Plutonium contains 94 protons and 150 neutrons. What is the magnitude of the force from the nucleus on a single electron that is a distance of 0.563x10-12 m from the Plutonium nucleus?

    So basically this was a homework question that I got wrong, and I'm not entirely sure what the correct answer is. I'm reworking it to study for an exam, but I want to make sure this is right so I don't keep lousing it up!

    2. Relevant equations

    e=1.60x10-19 C
    and F=kQ/r2
    where k is Coulomb's constant 8.99x109 Nm2/C2

    3. The attempt at a solution

    Okay so if there are 94 protons, there should be 94 electrons.
    (94)(e)=(94)(1.60x10-19 C)=1.5x10-17 C

    Where I'm getting confused is what charge I should use to find the force? Because 1.5x10-17 C is the charge of all 94 electrons and I need the magnitude of the force of the nucleus on just one electron. I'm not quite grasping this concept.

    Anyway, if I blindly plug in numbers without really understanding completely what I'm doing here, I get:

    F=(k(1.5x10-17 C))/(0.563x10-12 m)2
    so F=4.27x1017 N

    Also, how do I type fractions on this forum? I found the button but I'm not sure where to enter my numbers so it works! Thanks!
  2. jcsd
  3. Jan 30, 2013 #2


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    You've left something out of that equation.
    The problem asks for the force of the nucleus on a single electron. You can ignore the other 93 electrons.
  4. Jan 30, 2013 #3
    Okay, so should I have used F=[itex]\frac{(k(q1)(q2))}(r2){}[/itex]? And then I would use e as the charge of one electron (my q2) and the charge of all 94 electrons as my q1? Or am I completely off here? Thank you!
  5. Jan 30, 2013 #4
    Oh, sorry, the fraction thing still is not working for me. I meant F=(k(q1q2))/(r^2)
  6. Jan 30, 2013 #5


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    That's the way to do it.
  7. Jan 30, 2013 #6
    Oh!!!! Yay!!!! Thank you so much,tms! I really appreciate it!
  8. Jan 30, 2013 #7


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    You need to put the denominator in the second set of curly braces: \frac{(k(q1)(q2))}{(r2)}
    You should also use subscripts and superscripts, and you can get rid of the extraneous parentheses: F=k\frac{q_1q_2}{r^2}
    If you are planning to go further in math or science, it is worth learning LaTeX. You can google for some brief introductions and tutorials.
  9. Jan 30, 2013 #8
    I tried doing that, but it didn't look right when I previewed it. My browser can be kind of wonky, though, so I'll keep trying. And I've never heard of LaTeX--sounds really cool. I'll definitely google that! Thanks again for all your help!
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