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Homework Help: Two particles having charges separated by a distance

  1. Apr 22, 2008 #1
    Two particles having charges of 0.600 nC and 5.40 nC are separated by a distance of 1.30 m.

    A.) At what point along the line connecting the two charges is the net electric field due to the two charges equal to zero?

    the electric field is zero at a point _______ m from .600nC

    i found out the answer to this to be .325m. by doing the following:

    E due to q1 is equal in magnitude to E due to q2 but in opposite direction

    As both q1 and q2 are positive, the field is zero at a point in between them

    As distance from q1 is L , distance from q2 is (1.3 - L)

    kq1/L^2 = kq2/(1.2 - L)^2

    (1.3 - L) / L= sq rt (q2 / q1)

    (1.3 - L) = L* sq rt (q2 / q1)

    1.3 = L [1+sq rt (q2 / q1)]

    L = 1.3 / [1+sq rt (q2 / q1)]

    L = 1.3 / [1+sq rt (5.40 / 0.600)]

    L = 1.3 / [1+sq rt ( 9.00 )]

    L = 1.3 / [1+ 3.0]

    L = 1.3 / [ 4.0]

    L=0.325 meter from 0.550 nC

    Where would the net electric field be zero if one of the charges were negative.
    Enter answer as a distance from the charge initially equal 0.600 nC . This is where i get lost, i don't know what to do next. please Help!
  2. jcsd
  3. Apr 22, 2008 #2
    You do it like you did the first one. Start with
    [tex]\vec{E_1} + \vec{E_2} = 0[/tex]

    Be careful about the vector directions.
  4. Apr 23, 2008 #3
    should the answer be the same but just negative since i using the same values as before?
  5. Apr 23, 2008 #4
    When I wrote, "You do it like you did the first one," I meant, you start it the same way. The algebra is different.

    I apologize; I should have been clearer.
  6. Apr 24, 2008 #5
    Thanks A Bunch!
  7. Apr 24, 2008 #6
    You're welcome.
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