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: Find the Electric Field at a midway point

  1. Feb 25, 2012 #1
    The problem is:
    Find the electric field at a point midway between two charges of +30.0 x 10^-9C and +60.0 x 10^-9 C separated by a distance of 30 cm.

    I used E=k (Q/r^2)
    My attempt is:

    E=(9x10^9)(30.0 x 10^-9C)/(.3m^2)
    E=3000 N/C

    E=(9x10^9)(60.0 x 10^-9 C)/(.3m^2)
    E=6000 N/C

    added they are 9000 N/C. I am fairly certain this is incorrect, but I do not understand the material. I really have no idea why or how to go about finding the correct answer. Please help!
  2. jcsd
  3. Feb 25, 2012 #2
    I think you might want to try subtracting them like 6000-3000=3000.
    I think that electric fields go away from positive charges
  4. Feb 26, 2012 #3
    I still don't really understand. Is .3m really the right radius? It's the distance between the charges, but I'm not sure if it's the right radius to use. Any suggestions? :/
  5. Feb 26, 2012 #4


    User Avatar

    Staff: Mentor

    Always draw a diagram. If the two charges are separated by 30 cm, how far is the mid point from each charge? Pay attention to the directions of the fields that each charge produces at the given location.


    Attached Files:

  6. Feb 26, 2012 #5
    Thank you so so so much!! that was so helpful! I think I solved it correctly now. :) thanks so much!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook