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Electric Field due to multiple point charges

  1. Feb 11, 2017 #1
    1. The problem statement, all variables and given/known data

    Derive expressions for the magnitude and direction of the electric field at point P and the potential
    at R.

    Charges Q1 and Q2 are both positive. pointcharges.jpg

    Distance from Q1 to P is h, distance from Q2 to P is √2 h

    2. Relevant equations

    E = k q/r^2

    3. The attempt at a solution

    I started with finding E field at point P for each of the 2 charges, giving:

    E1 = k Q1/h^2

    E2 = k Q2/2h^2

    Then separate into x and y components.
    For E1, the x component is 0, and the y component is just the total E1.
    For E2, the x component is E2 * cos45 , and the y component is E2 * sin45. (I think.)

    Is it okay to give the answer as just (magnitude) x direction + (magnitude) y direction ?

    Or should the answer be given as just 1 number for magnitude, and one angle for direction? Wouldn't this give some horrible expression?
  2. jcsd
  3. Feb 11, 2017 #2


    User Avatar

    Staff: Mentor

    You should sketch in the vectors on the figure so that you can get an idea of the directions of the components. No doubt there's angles of 45° involved, but a sketch will help you to locate where those angles sit.
    If the question doesn't specify a preferred method then either format for a vector should be acceptable. You might find that the expression for the angle simplifies a good amount through cancellation of variables.
  4. Feb 12, 2017 #3
    Okay, thank you!
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