Three point charges + q, -2q and +q are placed at points (x = 0, y = a, z = 0), (x = 0, y = 0, z = 0) and (x = a, y = 0, z = 0), respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are

Electric dipole moment is a vector quantity directed from negative charge to the similar positive charge. Choose the three coordinate axes as x, y and z and plot the charges with the given coordinates as shown.O is the origin at which -2q charge is placed. The system is equivalent to two dipoles along x and y-directions, respectively. The dipole moments of two dipoles are shown in the figure. The resultant dipole moment will be directed along OP, where co-ordinates of P is (a, a, 0). The magnitude of resultant dipole moment isp'=p2+p2=(qa)2+(qa)2=2qa