Four objects W, X, Y and Z, each with charge +q are held fixed at four points of a square of side d as shown in the figure. Objects X and Z are on the midpoints of the sides of the square. The electrostatic force exerted by object W on object X is F. Then the magnitude of the force exerted by object W on Z is

Two charges 14 $$\mu$$C and $$-$$4 $$\mu$$C are placed at ($$-$$12 cm, 0, 0) and (12 cm, 0, 0) in an external electric field $$E = \left( {{B \over {{r^2}}}} \right)$$, where B = 1.2 $$\times$$ 10⁶ N/(cm²) and r is in metres. The electrostatic potential energy of the configuration is

Assertion (A) : A negative charge in an electric field moves along the direction of the electric field.

Reason (R) : On a negative charge a force acts in the direction of the electric field.

Equipotentials at a large distance from a collection of charges whose total sum is not zero are -