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Homework Help: Problem driving me insane electric forces

  1. Jun 21, 2004 #1
    When 2 identical ions are separated by a distance of 3.3*10-10m, the electrostatic force each exerts on the other is 8.5*10^-9N. How many electrons are missing from each ion?

    I know I have to use coloumb's law to get Q1Q2, but how do i get the number of electrons missing from each?
     
  2. jcsd
  3. Jun 21, 2004 #2

    Doc Al

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    Staff: Mentor

    The charges are identical, so Q1 = Q2 = Q. Solve for Q and figure out how many electron charges that it equates to.
     
  4. Jun 21, 2004 #3
    I solved for Q, but how do i convert to electron charges? Because Q comes out in Coloumb's squared
     
  5. Jun 21, 2004 #4

    Doc Al

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    Not if you did it correctly. Show me how you applied Coulomb's law and solved for Q.
     
  6. Jun 21, 2004 #5
    Q = F*r*r/k
    Q = 8.5*10^-9N *(3.3*10^-10m)^2/9.0*10^9 N*m^2/C^2
    Q = 1.0825*10^-19 C^2
    Q = square root of above = 3.207*10^-10C
    What do I do after that?
     
  7. Jun 21, 2004 #6

    Doc Al

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    These should read Q*Q =
    Recheck this answer for Q*Q.
    You made an arithmetic mistake in finding Q*Q.
     
  8. Jun 21, 2004 #7
    can u explain youself a little more, i don't understand what you are trying to say in the above post
     
  9. Jun 21, 2004 #8

    turin

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    Hopefully DocAl will forgive my intrusion:

    You are using the symbol, "Q," to represent Q1*Q2. But, if both Q1 and Q2 are equal to Q, then, upon substitution: Q1*Q2 = Q*Q.
    It is at the very least symbolically misleading to say: Q1*Q2 = Q.

    Anyway, once you get that straightened out, the charge will be in Coulombs. Then you need to use the charge of an electron in Coulombs: 1.6x10-19 C.
     
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