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Homework Help: Electric potential/electric fields

  1. Mar 5, 2008 #1
    1. The problem statement, all variables and given/known data

    two oppositely charged students bring thier fingers toward each other. a spark jumps between their fingers when brought 7.0 cm apart.

    A) what is the electric field between fingers when sparking occurs

    B) what is the potential difference between the two students

    2. Relevant equations

    f= kq1q2/r^2
    3. The attempt at a solution

    i think i can get part b if i get a
    but i dont really have aclue where to even start
    i know e=q/f
    but what does distance have to do with it??
    can someone help me where to start??
  2. jcsd
  3. Mar 5, 2008 #2
    i think you mean E = F/q....

    use the force which has the distance (r) as the distance where the sparking occurs.

    so F = (-kq^2)/(r^2), since they are oppositely charged particles...

    I think the rest is self explanitory, you can solve for E using the force equation F = Eq, and your done.

    for part b use the potential difference formula between the students. V = kq/r.
  4. Mar 5, 2008 #3
    but what is q

    can someone else please explain this
    i dont undersatnd fubag
  5. Mar 5, 2008 #4
    q should've been given, otherwise if you're assuming its an electron/proton type problem then use q =+/- 1.6 *10^-19 Coulombs...im not sure what the question is asking for
  6. Mar 5, 2008 #5
    ya q isnt given at all
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