electromagnetics 1?

Question

Find the force on the 100microC charge at (0, 0, 3)m if four like charges of 20microC are located on the x and y axis at ±4m....show solution....thnx

Answer 1

This one is fairly easy. Just by visualizing 4 charges equally distributed on a charge on the z-axis, you can see the direction of the pull will be dowh the z-axis; -k (where i, j and k are the unit vectors for x, y, and z)

The magnitude of the pull is easy, too. Since the forces from all 4 charges are symmetrical, we can analyze one of them and simply multiply be 4.

The distance between the 1st charge and one of the others is 5 meters (a 3, 4, 5 triangle). Coulombs law will give us the force. F = k0 * (q1 * q2) / r^2

where: k0 = 8.988E9 Newton * meter^2 / Coulomb^2

F = 8.988E9 * 100E-6 * 10E-6 / 25
F = 0.359 Newton

Multiply that by 4 (for each of the charges on the x-y plane)
F = -1.438 k Newtons (k in this case, is the unit vector).

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