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Homework Help: Electric potential (need help with angle)

  1. Nov 10, 2014 #1
    1. The problem statement, all variables and given/known data
    The electric potential of a region of space is V= 200 / sq root (x^2 + y^2), where x and y are in meters. What are the strength and direction of the electric field at (x,y) = (2m,1m)?

    2. Relevant equations

    3. The attempt at a solution
    I took the negative derivative of V to find what the electric field would be.

    Then i substituted in (2,1)
    200(2)(5)^-3/2 x + 200(5)^-3/2
    =35.78x + 17.89 y

    im having trouble figuring out where the angle should be. i do this a lot.

    if i take the arctan or tan-1 of Ey/Ex

    i get an angle of 26.6 degrees. Now is that 26.6 degrees ccw above the x-axis??
    im having trouble figuring out where the final electric field will end up.
    when i looked at the signs of x,y theyre both negative in the problem which means it would be quadrant 3.
    even when i do 360-26.6 it ends in quadrant 4 which doesnt make sense

    Please i dont need any help with the problem just with some help understanding the angle
  2. jcsd
  3. Nov 10, 2014 #2
    nevermind the x and y components are both positive so it falls in quadrant I.

    thread closed
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