done by an external force (equal and opposite to the electrostatic force) in bringing a charge q from a point R to a point P is V P – V R , which is the difference in potential energy of charge q between the final and initial points. . Potential at a point is the work done per unit charge (by an external agency) in bringing a charge from infinity to that point. Potential at a point is arbitrary to within an additive constant, since it is the potential difference between two points which is physically significant.
If potential at infinity is chosen to be zero; potential at a point with position vector r due to a point charge Q placed at the origin is given is given by ( ) o Q . The electrostatic potential at a point with position vector r due to a point dipole of dipole moment p placed at the origin is ˆ ( ) o p r FIGURE . Principle of construction of Van de Graaff generator.