Electric force line

Electric force lines are imaginary but the electric fields generated by them are real. A tangent drawn at any point to the electric field line represents intensity of the electric field at that point.

Properties of electric line of force

1. These lines run from positive charge and end at negative charge.

2. The tangent line drawn at any point on the electric force line shows the direction of the force acting on the positive charge at that point.

3. No two force lines can intersect each other because in that case two tangent lines can be drawn at the intersection point which will show two directions of force at that point. Which is impossible.

4. The intensity of the electric field depends on the number of electric field line.

Electric field intensity

The ratio of the force exerted on a test charge placed at any point in the electric field and the value of the test charge is called the intensity of the electric field at that point. It is represented by E. If the force acting on a test charge qₒ placed at any point in the electric field is F,

Then the intensity of the electric field at that point is,

E=[F/qₒ][N/C]

If,

qₒ=1

E=F.N/C

Therefore,

The electric force acting on a unit charge is called electric field intensity.

Unit and dimensions of electric field

Unit

[kg.m/sec²]/Coulomb

[kg.m/sec²]/Ampere.sec

Kg.m(A)⁻¹sec⁻³

Dimensions

MLA⁻¹T⁻³

Electric field intensity due to point charge

Consider a positive charge +q due to which the intensity of the electric field at a point P is to be calculated.

To find the intensity of electric field at point P,

Consider the positive test charge qₒ situated at that point.

Therefore,

Electric force on positive test charge qₒ

F = [1/4π€₀].[q.q₀/r²] Newton

E=F/qₒ

F = E.qₒ

E.qₒ = [1/4π€₀].[q.q₀/r²]

E = [1/4π€₀].[q/r²] N/C