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Homework Help: Electrostatic Force

  1. Mar 6, 2005 #1
    Three identical point charges of 2 micro C are placed on the x-axis. The first charge is at the origin, the second to the right at x = 50 cm (.5 m), and the third at the 100 cm (1 m) mark. What are the mag. and direction of the electrostatic force which acts on the charge on the origin?

    The answer is 0.18 to the left.

    I calculated the magnitude and got 0.18 by:

    finding F_12 and F_13, which is .144 N and .036 N, respectively.

    F_1 = F_12 + F_13 = .18 N,

    where 1 is charge at origin, 2 is charge at .5 m, and 3 is charge at 1m.

    Is this even correct at all? Why must F_12 and F_13 be added?
    How is the direction to the left?

  2. jcsd
  3. Mar 6, 2005 #2
    This is correct. The forces must be added because the electric field adds. You could also calculate the electric field from the 2 and 3 charges and then find the force. The force is to the left because 2 and 3 are to the right of 1 and like charges repell each other.
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