Electric Lines of Force

A very convenient method for depicting the electric field (or force) is to draw lines of force pointing in the direction of the field. The sketch of the electric field lines gives an idea of the magnitude and direction of the electric field. The number of field lines passing through a unit area of a plane placed perpendicular the direction of the field is proportional to the strength of the field. A tangent at any point on the field lines gives the direction of the field at that point.

The electric field lines are only fictitious construction to depict the field. No such lines really exist.

Field Lines of Point Charge

The field lines of a stationary positive charge point radially in outward direction. But for stationary negative charge, the lines start from infinity and terminate at the point charge in radially inward direction (towards the point charge).

Field Lines For Two Charges 

For two equal and similar positive charges placed close to each other, the lines are almost radial at points very close to the positive charges and repel each other, bending outwards.

Properties of Electric Field Lines

• The field lines start from a positive charge radially outward in all directions and terminate at infinity.
• The field lines start from infinity and terminate radially on a negative charge.
• For a dipole, field lines start from the positive charge and terminate on the negative charge.
• A tangent at any point on field line gives the direction of electric field at that point.
• The number of field lines passing through unit area of a surface drawn perpendicular to the field lines is proportional to the field strength on this surface.
• Two field lines never cross each other.