In the figure below, a central particle of charge -2q is surrounded by a square

Question

In the figure below, a central particle of charge -2q is surrounded by a square array of charged particles, separated by either distance d or d/2 along the perimeter of the square. http://www.webassign.net/hrw/22_14.gif

(a) What is the magnitude of the net electrostatic force on the central particle due to the other particles?

a.8q2/40d2

b.q2/40d2

c.4q2/40d2

d.6q2/40d2

(b) What is the direction of the net electrostatic force on the central particle due to the other particles? (Hint: Consideration of symmetry can greatly reduce the amount of work required here.)

a.rightward downward

b.leftward upward

Explanation / Answer

a)

electric force at center by -7q will be cancled by another -7q and also electric force by +2q will be cancled by another +2q and electric force by +4q will be cancled by another +4q and electric force by -5q will be cancled by another -5q and electric force by -3q will be cancled by another -3q. only electric force by +3q will be effected at center.

so Net electric force at center due to +3q = F = (2q)*(3q)/[4*pi*e0*(d)^2] = 6*q^2/[4*pi*e0*(d)^2]

so Answer is (D).

b)

Direction of Net electric force = Direction of electric force due to +3q

so Direction of Net electric force is leftward (attractive force)

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