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Basic Electric Field Question

  1. Dec 14, 2008 #1
    1. The problem statement, all variables and given/known data

    i Can't seem to get the right answer :

    A Particular dipole consists of two charges of magnitude 6.0 x 10^-12 C. If the charges are sperated by a distance of 5.0 cm, determine the size and direction of the electric field at the midpoint between the charges.


    2. Relevant equations

    E= Q / [4(3.14) x (8.85 x 10^-12) x r^2 ]

    3. The attempt at a solution

    E= [(6.0 x 10^-12)^2] / [4(3.14) x (8.85 x 10^-12) x (0.05)^2]
    = 1.29 x 10^-10

    but the answer is 1.7 x 10^2 N/C
    So i mut be missing something or im just doing it all wrong
     
  2. jcsd
  3. Dec 14, 2008 #2

    hage567

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    Homework Helper

    Your equation is not consistent throughout your calculation (you go from Q to Q2).

    You are trying to find the electric field at the midpoint between the charges; not at the location of one charge (so the r value you are using is wrong).

    You must sum up the contribution from each charge at the midpoint.
     
  4. Dec 14, 2008 #3
    Thanks for the reply but I am having trouble understanding the whole charge concept, how do we sum up the contirbution of each charge?
     
  5. Dec 14, 2008 #4

    hage567

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    Homework Helper

    Take the electric field due to a point charge equation: E = kQ/r2
    This is a vector, so the total electric field at the midpoint will be Etotal = E1 + E2
    It's a dipole arrangement, so one charge is negative and one charge is positive. This tells you the direction of the electric field due to that charge.

    See http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elefie.html#c2
     
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