An electric field is defined as any region around a charge in which an electric test charge would experience an electric force.

The concept of field theory was introduced by Michael Faraday. He stated that the charge q produces an electric field in the space surrounding it and when a charge qo is brought in its field then it exerts a force F on it. The electric field around a charge is like a sphere with in which other charges are influenced by it.

The existence of electric field can be proved by bringing a test charge qo into its field.

**Equation **

The force F experienced by a test charge qo , is given by

F= qo E.

It is a vector field so it is characterized by strength and direction at every point in space. The strength and direction of it can be determined by placing a unit positive test charge in that field. The strength of the field at a point in space determines the amount of the force that a charge will experience if it is placed at that point. The direction in which this unit positive test charge move or tends to move is the direction of electric field.

**Electric Field Intensity **

A single vector quantity containing information about the field strength and its direction at that point is denoted by E and is known as electric field intensity. Thus the field strength is the magnitude of the force expressed by the unit positive test charge placed at that point.

**Defination **

lf unit positive test charge qo experience a force F due to the electric field of charge q. Then the intensity of E at any point is the force per unit positive test charge placed at that point.

**Equation **

The electric field intensity

Ē= F/qo

or

F =qoĒ

Electric field strength is also a vector quantity. The test charge is so small that it does not distort the original field due to the primary source. The SI unit of E is newton per coulomb (N/C) or volt per metre (V/m).

In order to find out the field intensity due to a point charge q. A positive test charge q, is placed at a distance r from point charge q .Then by coulomb’s law the force experienced by a unit positive test charge qo due to the field of a point charge.

F = kqqo / r2

As r` is the unit vector directed from charge q to qo, so in vector form

F = kqqor`/r2

so the E is given by

Ē = F/q = k(qqo)r`/qor2

Ē=kqr`/r2

The strength of the field is proportional to the magnitude of the source charge. Its strength decrease as the teat charge moves away from source charge q.

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