1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Calculating charge when given electric field

  1. Jan 7, 2012 #1
    1. The problem statement, all variables and given/known data

    Charges of 5 µC are located at x = 0, y = 2.0 m and at x = 0, y = -2.0 m. Charges Q are located at x = 4.0 m, y = 2.0 m and at x = 4.0 m, y = -2.0 m. The electric field at x = 0, y = 0 is (9e3 N/C) . Determine Q.

    2. Relevant equations

    E = kQ/r^2

    3. The attempt at a solution

    I converted my units to C so I could use the k constant of 8.99e9 N*m^2/C^2
    I know that all the vertical components get cancelled out so the only force is the the x positive direction.

    I set up my equation like this E= kQ/r^2 with E being 9e3 and r^2 being 20

    I end up with 9e3=kQ/10 and when I solve for Q I get 1e-5 C and when I convert my answer to microcoloumbs I get 10.

    I think I am having problems with my conversions. Any help would be greatly appreciated!!
  2. jcsd
  3. Jan 7, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Hello jakethelocker. Welcome to PF !

    Don't forget that E is a vector quantity. Look at the x and the y components of the field due to the Qs.
  4. Jan 7, 2012 #3
    I got it! Thank you for your help :)
    Last edited: Jan 7, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook