Page 2 - Lesson Note - 1

mid-point of dipole is given by

7. The electrostatic potential on the perpendicular bisector due to an electric dipole is zero.
8. Electrostatic potential at any point P due to a system of n point charges q 1, q 2, ……………,
q n whose position vectors are r 1,r 2,…,r n respectively, is given by

where, r is the position vector of point P w.r.t. the origin.
9. Electrostatic potential due to a thin charged spherical shell carrying charge q and radius R
respectively, at any point P lying

10. Graphical representation of variation of electric potential due to a charged shell at a distance
r from centre of shell is given as below:

11 Equipotential Surface A surface which have same electrostatic potential at every point on it, is
known as equipotential surface.
The shape of equipotential surface due to
(i) line charge is cylindrical.
(ii) point charge is spherical as shown along side:
(a) Equipotential surfaces do not intersect each other as it gives two directions of electric field E at
intersecting point which is not possible.
(b) Equipotential surfaces are closely spaced in the region of strong electric field and vice-versa.
(c) Electric field is always normal to equipotential surface at every point of it and directed from one
equipotential surface at higher potential to the equipotential surface at lower potential.