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!

Charges: Electirc forces

  1. Apr 6, 2010 #1
    1. The problem statement, all variables and given/known data
    Three point charges lie in a straight line along the y-axis. A charge of q1 is -9 microcouloumbs at y = 6 m and a charge of q2 is -8 microcoulombs at y = -4m. The net electric force on the third point charge is zero. Where is this charge located.

    2. Relevant equations

    Fe = k (q1*q2/r^2)

    3. The attempt at a solution

    Fe = k (q1*q2/r^2)
    = (9*10^9)((9*10^-6)(8*10^-6)/(10m)^2))
    = 6.5*10^-3 N

    Then i attempted to plug in this value for Fe to receive the r, and the location, but
    i don't know which two charges i had to use.


  2. jcsd
  3. Apr 6, 2010 #2


    User Avatar
    Homework Helper

    What's the equation for the electric field? Do you know how to add electric fields induced by different charges?
  4. Apr 6, 2010 #3
    I know how to add different electrical forces, but the problem i have is finding the location of it, instead of the force.
  5. May 3, 2010 #4


    User Avatar
    Homework Helper
    Gold Member

    So you've added the two equations for the electric fields of the first two charges together, giving you an equation for the overall electric field E as a function of y (considering both charges). What location along y produces a zero electric field? (Hint: you need to set something to zero and solve for y.)

    If a charge is in a zero electric field, what can you say about the net electric force acting on that charge? :wink:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Charges Electirc forces Date
Making Capacitance the subject of discharge equation Yesterday at 3:33 PM
Finding the charge density that produces a specific field Yesterday at 7:15 AM
Find the charge of Capacitor 2 in the circuit Tuesday at 8:55 AM
Charged pendulum in magnetic field Saturday at 12:36 PM
Question about electirc field Mar 14, 2013