1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric Field Vector Resulting from Two Point Charges (not getting right answer)

  1. Apr 19, 2015 #1
    1. The problem statement, all variables and given/known data
    A +20nC point charge is placed on the x axis at x = 2.0 m, and a -25 nC point charge is placed on the y axis at y= -3.0 m. What is the angle that the direction of the electric field at the origin makes with the x-axis.

    (a) 209 (deg)
    (b) 61 (deg)
    (c) 29 (deg)
    (d) 241(deg)
    (e) 119 (deg)

    2. Relevant equations

    E = ke(q/r^2)

    3. The attempt at a solution

    E= (8.99x10^9) [ (20x10^-9)/4 (i) - (25x10^-9)/9 (j)]
    = (8.99x10^9) [ 5.0x10^-9 (i) - 2.78x10^-9 (j)]
    = 44.95i - 24.97j
    = 51.42

    The angle between the x-axis is arccos(44.95/51.42) = 29 (deg)

    But the correct answer is 209 (deg).
     
  2. jcsd
  3. Apr 19, 2015 #2

    berkeman

    User Avatar

    Staff: Mentor

    Check the sign of your first term. Which way does the E field at the origin point when you have a positive charge at x=2m? :smile:
     
  4. Apr 19, 2015 #3
    Oh makes sense, thank you !:)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Electric Field Vector Resulting from Two Point Charges (not getting right answer)
Loading...