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: Finding Electric Field at point P

  1. Jan 29, 2012 #1
    1. The problem statement, all variables and given/known data
    Two charges are located in the (x, y) plane as
    shown. The fields produced by these charges
    are observed at a point p with coordinates
    (0, 0). Find the x-component of the electric field
    at p. The value of the Coulomb constant is
    8.98755 × 109 N · m[itex]^{2}[/itex]/C[itex]^{2}[/itex].
    Answer in units of N/C

    2. Relevant equations
    k[itex]_{c}[/itex] = 8.98755E9
    cos θ[itex]_{12}[/itex] = [itex]\frac{1.7}{sqrt(8.65)}[/itex]
    cos θ[itex]_{13}[/itex] = [itex]\frac{1.6}{sqrt(8.32)}[/itex]
    q[itex]_{2}[/itex] = -8.1 C
    q[itex]_{3}[/itex] = 7.9 C
    r[itex]_{12}[/itex] = [itex]sqrt(8.65)[/itex]
    r[itex]_{13}[/itex] = [itex]sqrt(8.32)[/itex]

    3. The attempt at a solution
    E[itex]_{x}[/itex] = -(k[itex]_{c}[/itex]|q[itex]_{2}[/itex]|cos θ[itex]_{12})/r_{12}^{2}[/itex] - (k[itex]_{c}[/itex]|q[itex]_{3}[/itex]|cos θ[itex]_{13}[/itex])/r[itex]_{13}[/itex][itex]^{2}[/itex]

    = -k[itex]_{c}[/itex]([itex]\frac{8.1}{8.65}[/itex] * [itex]\frac{1.7}{sqrt(8.65)}[/itex] + [itex]\frac{7.9}{8.32}[/itex] * [itex]\frac{1.6}{sqrt(8.32)}[/itex])

    is this the right way to do it?

    Attached Files:

    Last edited: Jan 29, 2012
  2. jcsd
  3. Jan 29, 2012 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Hard to say since you didn't show or describe the locations of the charges ...
  4. Jan 29, 2012 #3
    sorry here is the picture
  5. Jan 29, 2012 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member


    Not quite alright.

    Where are the angles, θ12 , θ13 ?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook