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Homework Help: Electric Field

  1. Jan 26, 2010 #1
    1. The problem statement, all variables and given/known data

    The electric field strength 8.05 cm from a very long charged wire is 1310 N/C. What is the electric field strength (in N/C) 30.0 cm from the wire?

    2. Relevant equations
    E=F/Q
    E=KQ/R^2


    3. The attempt at a solution
    First I try to find the charge using E=KQ/R^2
    1320=K(Q)/(8.05)^2
    Q= 9.432 x 10^-6

    second I used the charge to find the electric field.
    E= k(9.432 x 10^-6)/30^2
    E= 94.32 N/C

    I didn't convert cm to m because it would cancel out at the end.
    so I don't know why my answer is still wrong.Any help will be great.
    thanks guys.
     
  2. jcsd
  3. Jan 26, 2010 #2
    You are assuming the wire is a point charge, which it is not. You would have to integrate:
    2 (Integral from 0 to infinity) kdq/r^2
    I hope you know what to do from there
     
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