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Please help electric field and electric potential

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data
    One positive (+2q) and two negative (-q) charges are arranged as displayed in fgure 1.
    Calculate electric feld E and electric potential (a) at points along the positive y¡axis as
    functions of their coordinate y. What is the direction of E at those points? In your results,
    does y-component Ey of the field satisfy Ey = -dx/dy? Is it supposed to satisfy?

    x
    -q...................................2q...................................q)

    2. Relevant equations

    E = ke q/r^2


    3. The attempt at a solution

    i dont know how to start this problem.
     

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    Last edited: Sep 23, 2007
  2. jcsd
  3. Sep 23, 2007 #2

    malawi_glenn

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    I do not understand your picture..
     
  4. Sep 23, 2007 #3
    i added the picture
     
  5. Sep 23, 2007 #4

    malawi_glenn

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    Then the electric field is force/ unit charge.

    So you should add all forces that comes from the 3three charges; note their signs! ; as a function of y.

    What is the distance from point y to x ? (i.e the r in the formula), hint: triangle..
     
  6. Sep 23, 2007 #5
    i will try that thank you.
     
  7. Sep 23, 2007 #6
    so for the first part, i got

    E = -4ke/a^2
    is that all or can i solve this further?
     
  8. Sep 23, 2007 #7

    malawi_glenn

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    where did the 4 come from? And it should be a function of y, and i forgot: Use also vectors. i.e for a certain point on the y-axis, find the x and y composant of the force for each charge, then add x and y-wise; so you get the direction too.
     
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