Gravitational and electric forces are not contact forces. Objects do not have to touch for these forces to act. They can act over a distance.

To explain how these forces can act over a distance, scientists devised the idea of field. The field refers to the region of space surrounding an object. In the case of electric field, whereby the field extends outward from every charge and permeates all space. When a second charge is placed in this field, it feels a force, because of the electric field at that point.

We define the electric field at a location of the small test charge (unit positive charge) to be the electric force acting on it divided by the charge q _o of the test charge:

Electric field = electric force/electric charge

Or E = F/ q _o ……………………. (2-1)

Or F = q _o E

Where F = Force

q ₀ = Positive unit test charge

E = Electric field

Note that this is the electric field at the location of q _o produced by the charge Q, not the field produced by q _o. The electric field is a vector quantity, and has SI units (N / C,), or equivalent to (V/m). The direction of the electric field is defined to be the direction of the electric force that would be exerted on a unit positive test charge placed at that point.

The isolated conductor has the following properties:

1. The electric field is zero inside the conducting material.

2. Any excess charge on an isolated conductor resides entirely on its surface.

3. The electric field just outside a charged conductor is perpendicular to the conductor's surface.

4. On an irregularly shaped conductor, the charge accumulates at locations where the radius of the curvature of the surface is smallest - that is, at sharp points.