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Homework Help: What is the the electric field at a point midway between

  1. Jan 21, 2010 #1
    1. The problem statement, all variables and given/known data
    What is the the electric field at a point midway between a -7.39 uC and a +5.17 uC charge 3.32 cm apart? Take the direction towards the positive charge to be positive.


    2. Relevant equations
    E1=kq1/r^2
    E2=kq2//r^2
    E1+E2=Etotal


    3. The attempt at a solution
    E1=8.9E9(5.17E-6)/.0332^2
    E2=8.9E9(-7.39E-6)/.0332^2
    I got 4.1E7 and 5.97E7 which i added up for 1.014E8 N/C
     
  2. jcsd
  3. Jan 21, 2010 #2

    fluidistic

    User Avatar
    Gold Member

    Are you sure you didn't make a sign error for E2?
    Also, the charges are 3.32 cm apart. You are situated midway through them. How could then r be 3.32 cm?
     
  4. Jan 21, 2010 #3
    wow thanks, i didnt even think about how it was in the middle. thanks again so much
     
  5. Jan 21, 2010 #4
    I'm working on this problem also, and getting something wrong. I'm using the same equation as you. Did you find that dividing r/2 gave you the correct answer?
     
  6. Jan 21, 2010 #5
    um....ya. so i just divided the r by 2. but u still have to make sure you are squaring it? post up ur numbers and stuff and what you get if you are still having trouble and ill see if i can help you out
     
  7. Jan 21, 2010 #6
    What is the the electric field at a point midway between a -7.79 uC and a +5.66 uC charge 3.74 cm apart? Take the direction towards the positive charge to be positive.

    So I did:

    (9E9)(-7.79E-6)/(.00187^2)

    and

    (9E9)(5.66E-6)/(.00187^2)

    then added the two answers together, which isn't working.
     
  8. Jan 21, 2010 #7
    sorry it took so long, i had a class. it would be .0187 not .00187. that is probably why. does that work now?
     
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