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Homework Help: Electric Force and Charged Spheres

  1. Jan 10, 2007 #1
    1. The problem statement, all variables and given/known data

    Consider the following configuration of fixed, uniformly charged spheres on an xy coordinate system:
    ·a blue sphere fixed at the origin with positive charge q.
    ·a red sphere fixed at the point (d1,0) with unknown charge q_red,
    ·a yellow sphere fixed at the point (d2*cos theta, -d2*sin theta) with unknown charge q_yellow.

    The net electric force on the blue sphere is observed to be vector F = (0,-F), where F>0 .

    Here is a makeshift sketch:

    O = charged particle

    O_(q)___________O (d1, 0) q_red
    ----\O (d2*cos theta, -d2*sin theta) q_yellow

    in which the dotted line between q at (0,0) and q_yellow is d2 and theta = angle between d2 and the x-axis (The x- axis is depicted by __________ pattern.)

    What is the sign of the charge on the yellow sphere?
    What is the sign of the charge on the red sphere?

    2. Relevant equations

    Possibly Coulomb’s Law:

    F_mag = (k*|q1*q2|)/(r^2), where k = 8.988 * 10^9 N*m^2/C^2

    3. The attempt at a solution

    The y-component of the electric force is –F. The q_red particle does not have a y-component; it only has an x-component. The q_yellow charge has a y-component. If a – sign follows, then the q_yellow chage is positive since – indicates repulsion????

    Is the q_red charge negative? If the electric force’s x-component is 0, then q_red’s x-component must be negative if q_yellow’s x-component is positive???

    Last edited: Jan 10, 2007
  2. jcsd
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