Question
Three points 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
along + y direction
along the line joining point
qa along the line joining points (x = 0,y = 0, z = 0) and (x = a, y = a, z = 0)
along + x direction
Solution
B.
along the line joining point
0 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 figure 
The resultant dipole moment will be directed along OP where P = (a, a, 0). The magnitude of resultant dipole moment is
p' =
=
p' =
