Question -
Answer -
Four charges of same magnitude are placed at points X, Y,Y, and Z respectively, as shown in the following figure.
A point is located at P, which is r distanceaway from point Y.
The system of charges forms an electric quadrupole.
It can be considered that the system of the electricquadrupole has three charges.
Charge +q placed at point X
Charge −2q placed at point Y
Charge +q placed at point Z
XY = YZ = a
YP = r
PX = r + a
PZ = r − a
Electrostatic potential caused by the system of threecharges at point P is given by,
Since
is taken as negligible.
It can be inferred thatpotential, 
However, it is known thatfor a dipole, 
And, for a monopole, 