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Figure 18.13a shows three point charges that lie along the x axis in a vacuum. Determine the magnitude and direction of the net electrostatic force on q1.
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(a) Three charges lying along the x axis. (b) The force exerted on q1 by q2 is F12, while the force exerted on q1 by q3 is F13. |
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Reasoning
Part b of the drawing shows a free-body diagram of the forces that act on q1. Since q1 and q2 have opposite signs, they attract one another. Thus, the force exerted on q1 by q2 is F12, and it points to the left. Similarly, the force exerted on q1 by q3 is F13 and is also an attractive force. It points to the right in Figure 18.13b. The magnitudes of these forces can be obtained from Coulomb’s law. The net force is the vector sum of F12 and F13.
Solution
The magnitudes of the forces are
Since F12 points in the negative x direction, and F13 points in the positive x direction, the net force F is
The plus sign in the answer indicates that the net force points to the right in the drawing.
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