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Force and Torque exerted on a dipole system from a point charge

  1. Mar 21, 2012 #1
    I have attached a diagram.
    s
    Three charge are at corners of an triangle. The + and - 5.00*10^-6C charges form a dipole.
    a) Find the magnitude and direction of the force exerted on the dipole from the -10*10^-6C charge.
    b) For an axis perepndiculat to the line connected the + and - 5.00*10^-6C charges , find the torque exerted on the dipole by the -10*10^-6 C charge, direction and magnitude?


    My attempt:
    a) The net force = 0.
    Its magnitude on both charges = 1125 N, (from Coloumb's law and using r as 2cm.

    However the answer is 1680N on both charges respectively.

    b) Torque = Force * distance perpendicular to the line of action.

    Considering a single charge, the force exerted on it is 1125N, and the distance perpendicular to the line of action 1.5cm.

    The net torque will then = 2(1.5*10^-2 * 1125) , as the force acts in opposite directions on both charges, consequently rotating the dipole system in the same way.

    T = 33.75N.m

    (The correct answer is however 22.3N.m)F
     

    Attached Files:

  2. jcsd
  3. Mar 21, 2012 #2

    ehild

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    Homework Helper
    Gold Member

    The question is the force exerted on the whole dipole. You have to add the forces exerted on the separate charges, taking their directions into account.

    ehild
     
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