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!

Field due to point charges - extremely strange error

  1. Oct 10, 2014 #1
    1. The problem statement, all variables and given/known data
    Find electric field anywhere on the x axis due two two point charges
    Q at (0,0,d)
    -Q at (0,0,-d)

    2. Relevant equations


    3. The attempt at a solution
    Attached


    Somehow I am not getting the correct answer. I reviewed my steps with 4 people and we could not find the error!

    I'm starting to think I've ruined the laws of physics.
     

    Attached Files:

  2. jcsd
  3. Oct 10, 2014 #2

    NascentOxygen

    User Avatar

    Staff: Mentor

    Because you know one charge to be -Q then I would expect on the diagram you'd show its field line vector directed towards the charge.
     
  4. Oct 10, 2014 #3

    berkeman

    User Avatar

    Staff: Mentor

    What is the z-component of E?
     
  5. Oct 10, 2014 #4
    N.O. - The change in sign and direction was accounted for on the second line.
    berkeman - the answer I got was -2q/4piEo * 1/(x2 + d2) az which is different from the "correct" answer by a factor of d/(x2 + d2)
     
  6. Oct 10, 2014 #5

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    It is hard to read that image.

    You set up a vector and then write "=0." If that would be true, there would be nothing left to calculate.

    Where do you calculate the z-component of your force?
     
  7. Oct 10, 2014 #6
    Please discard that =0

    I rewrote the solution for clarity
     

    Attached Files:

  8. Oct 10, 2014 #7
    P/S. There a missing 2 one line before the end but it should be obvious
     
  9. Oct 10, 2014 #8

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    I don't see what you did in the numerator between the first and second line. Your new numerator has both a different magnitude and direction.
    You can make this way easier by combining the fractions and sorting the numerator by x and z components.
     
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: Field due to point charges - extremely strange error
Loading...