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 and total energy

  1. Jan 30, 2007 #1
    1. The problem statement, all variables and given/known data

    Two point charges lie along the y axis. A charge of q1 = -12.0 µC is at y = 7.0 m, and a charge of q2 = -2.0 µC is at y = -4.0 m. Locate the point (other than infinity) at which the total electric field is zero.

    2. Relevant equations

    E = (K lql) / r^2

    3. The attempt at a solution

    I setup the two equation make E = 0

    (K lq1l) / (7-y)^2 = (K lq2l) / (-4+y)^2

    It's wrong, plz correct my equation
  2. jcsd
  3. Jan 30, 2007 #2


    User Avatar
    Homework Helper

    Why do you think that equation is wrong?
  4. Jan 30, 2007 #3
    I think the equation is wrong because I double checked all my math and it said that the answer is wrong.
  5. Jan 30, 2007 #4


    User Avatar
    Homework Helper

    Ok, Let's review again:

    The point in which the electric field will be 0 is between the charges. Because of the standard convention. You picked a point inside so it's correct.

    Next we have to set our electric field vectors, such that:

    [tex] \vec{E}_{1} + \vec{E}_{2} = \vec{0} [/tex]

    [tex] \vec{E}_{1} = K \frac{|q_{1}|}{(7-y)^{2}} \vec{j} [/tex]

    [tex] \vec{E}_{2} = -K \frac{|q_{1}|}{(4+y)^{2}} \vec{j} [/tex]

    so, the error was using -4, because r will be a distance.
    Last edited: Jan 30, 2007
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Electric Field and total energy
  1. Total Electric Field (Replies: 1)