Electric Field
Electric field due to an Electric Charge can be defined as
The region or space around an electric charge in which any other charge experiences an Electric Force is called as electric field. OR The region or space around an electric charge within which its influence can be felt by any other charge is called as electric field. 
 The charge which produces the electric field is called as a source charge.
 The charge which tests the effect of source charge is called as a test charge.
Electric Field Intensity
The electric field intensity at any point is the strength of electric field at that point. It is defined as the force experienced by a unit positive charge placed at that point. 
If F is the force acting on a small test charge q_{0} at any point, then electric field intensity at this point is given by
(Equation01)
Since the charge q_{0} may disturb the electric field of the source charge, so the test charge q_{0} must be small enough.
It is better to define electric field intensity at a point as the force per unit test charge acting on a vanishingly small positive test charge placed at that point.
Hence,
It is important to note that the term electric field intensity is interchangeably used with the term electric field.
Direction of Electric Field
We have
(From Equation01)
The direction of electric field is same as the direction in which the test charge tends to experience the force.
Always Remember
The direction of electric field at any point is always along the line joining the source charge and the observation point.

Unit of Electric Field
As the electric field is force per unit charge, so its SI unit is newton per coulomb (NC^{1}).
Dimensional Formula of Electric Field
As the electric field is force per unit charge, so its dimensional formula can be derived as
Force on Charge In An Electric Field
We know, if F is the force acting on a small test charge q_{0} at any point, then electric field intensity at this point is given by
(From Equation01)
From here, the force F on a charge q in a uniform electric field having electric field intensity E is given by
(Equation02)
Important Notes

Acceleration of Charge In An Electric Field
We know, the force F on a charge q in a uniform electric field having electric field intensity E is given by
(From Equation02)
Important Notes

Electric Field Intensity Due To A Point Charge
Consider a source point charge Q placed at point O. We wish to calculate the electric field intensity at point P located at distance r from it.
We place a small test charge q_{0} at point P as shown
By Coulomb’s law, the magnitude of force experienced by the test charge q_{0} is given by
The magnitude of electric field intensity at point P is given by
Substituting the value of F, we get
On solving, we get
 We use the above formula for finding the magnitude of electric field intensity due to a point charge at a distance r from it.
 The direction of electric field is same as the direction in which the test charge tends to experience the force.
Graph
The following graph shows the variation of electric field intensity due to a point charge with distance from it
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Electric Field Lines  Properties
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