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!

Electric Field and charged plane

  1. Mar 12, 2014 #1
    1. The problem statement, all variables and given/known data

    An infinite, charged plane/plate has a uniform positive charge density of σ. Another positively charged particle is found at a distant of D from the plane. In point P, positioned between the two, the electric field equals 0.
    A. What is the distance between point P and the charged particle q?
    B. The plane is removed and replaced with a new positively charged particle Q. What should be the value of Q in point A in order for the electric field to remain 0?

    2. Relevant equations

    E=σ/2ε , E=k * Q/r^2

    3. The attempt at a solution

    In A, I've calculated the electric field the plane exerts on point p, which is E=σ/2ε, and then added the electric field exerted by particle q, which is E=k * Q/(D-r)^2.
    E=k * Q/(D-r)^2 + σ/2ε =0
    then found r. Am I right on this? Please help.

    In B, just use this equation E=k * Q/r^2 instead of E=σ/2ε, correct?
     

    Attached Files:

    Last edited: Mar 12, 2014
  2. jcsd
  3. Mar 12, 2014 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hi Hitch, and welcome to PF.

    Good use of the template, clear statements and I think your attempt is good. I wouldn't approach it any different -- although: Did you find an imaginary r ? Because everything I see in the expression looks positive...

    Tackling B in the way you propose is fine, too.
     
  4. Mar 12, 2014 #3
    Thanks :)

    How would you find the distance from point P to the particle q? I've thought of another way: maybe use a new variable such as x, and then subtract x from D, as in E=k * Q/x^2 ; distance from p= D-x?
    I'm unsure.
     
    Last edited: Mar 12, 2014
  5. Mar 12, 2014 #4

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You have already found this distance , namely in part A. You called it r.
    Now you want to calculate what charge is needed to create the same field at point P as the plate did. Not so difficult!
     
  6. Mar 12, 2014 #5
    So in B I use E=k * Q/(D-r)^2 with r, the distance I found in A. Thanks again!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted