What is electric field strength or electric field intensity ?

 All the materials are made up of atoms which contains subatomic particles (charged particles) such as :

1. Electrons (negative charge)
2. Protons (positive charge)
3. Neutrons (neutral)

• If an atom contains large number of electrons as compared to protons, it is said to be negative charged, And if the atom contains large number of protons as compared to electrons, it is said to be positive charged.

As we know that,

• Every electric charge has an electric field associated with it, which is represented by electric lines of force.The strength of the electric field is different at different points in the electric field. The strength of the electric field is called electric field strength or electric field intensity or electric intensity.
• It is usually denoted by E.
• It is a vector quantity. 

(Vector quantity - a quantity  that has both magnitude and direction.)

• The unit is newton/coloumb (N/C).

• If a Q1 coloumb of charge placed at a point in an electrostatic field experiences a force of F newton, then electric field intensity E at that point is given by

E = F/Q1 N/C

• Consider a body charged at (+Q) coulomb. It is required to determine electric field intensity at a point P at a distance of metres away from the charge body.
• Place a unit positive charge (+1C) at a point P as shown in figure. Then, the force acting on this unit positive charge will be the electric field intensity at that point.
• According to Coloumb's Second Law,

 

• The direction of electric field intensity is determined by Coloumb's first law.