ELECTRIC FIELD

 Transmission of Electric Field 

To describe the mechanism by which electric force is transmitted, Michael Faraday (1791-1867) introduced the concept of an electric field. According to his theory, it is the intrinsic property of nature that an electric field exists in the space around an electric charge. 

Force Field

The electric field is considered to be a force field that exerts a force on other charges placed in that field. For example, a charge q produces an electric field in the space surrounding it. This field exists whether the other charges are present in space or not. 

Presence of Electric Field 

The presence of field cannot be tested until another charge q0, is brought into the field. Thus the field of charge q interacts with q0, to produce an electrical force. The interaction between q and q0, is accomplished in two steps: 

(a) the charge q produces a field 

(b) the field interacts with charge q0, to produce a force F on q. 

These two steps are illustrated in Figure.

In this figure the density of dots is proportional to the strength of the field at the various points. We may define electric field strength or electric field intensity E at any point in the field as where F is the force experienced by a positive test charge q. placed at the point. The test charge q0, has to be very small so that it may not distort the field which it has to measure.

E = F/q0 ......... (1)

Since electric field intensity is force per unit charge, it is measured in newton per coulomb in SI units. It is a vector quantity and its direction is the same as that of the force F.

Place a positive test charge q0, at this point. The Coulomb's force that this charge will experience due to q is

where r is a unit vector directed from the point charge q to the test point where q0, has been placed, i.e., the point where the electric intensity is to be evaluated. By Eq.