Electric potential

 Infomation about the field may be given by stating the field strength at any point; alternatively the potential can be quoted.

In general work must be done to move a charged object A towards another object B that has the same type of charge. Their electric potential energy increases as A moves towards B. The electric potential energy of A increases from 0 if it is moved from infinity to B. The electric field of B causes a force of repulsion to act on A and this force must be overcome to move A closer to B.

The electric potential at a certain position in an electric field is the work done per unit positive charge on a 'positive test charge' when it is moved from infinity to that position. The unit of electric potential is the volt (V), equal to 1 JC^-1.

Potential is a property of a point in a field and is a scalar since it deals with a quantity of work done or potential energy per unit charge.

A positive charge in an electric field moves from a point of higher electric potential to one of lower potential.

Equipotentials:

All points in a field that have the same potential can be imagined as lying on a surface - called an equipotential surface. When a charge moves on such a surface no energy transfer occurs and no work is done. The force due to the field must therefore act at right angles to the equipotential surface and field lines always intersect at right angles.

Potential gradient:

The potential gradient at any position in an electric field is the change of potential per unit charge of distance in a given direction.

1) If the field is non-uniform, the potential gradient varies according to position and direction. The closer the equipotentials are, the greater the potential gradient is at right angles to the equipotentials.

2) If the field is uniform, such as the field between the two oppositely charged parallel plates, the equipotentials between the plates are equally spaced lines parallel to the plates. The potential gradient is constant, increases in the opposite direction to the the electric field and is equal to V/d.

The electric field strength is equal to the negative of the potential gradient.