Electric Field Lines and Properties of Electric Field Lines

Electric field lines : The concept of field lines was introduced by Michael Faraday asan aid in visualizing electric and magnetic fields.

Electric field lines are thus a way of pictorially mapping the electric field around a configuration of charges. 

Fig. Field of a point charge

An electric field line is, in general, a curve drawn in such a way that the tangent to it at each point is in the direction of the net field at that point. 

An arrow on the curve is obviously necessary to specify the direction of electric field from the two possible directions indicated by a tangent to the curve. A field line is a space curve, i.e., a curve in three dimensions.

Fig. Electric Field Lines

Properties of Electric field lines :

1. The field lines of a single positive charge are radially outward while those of a single negative charge are radially inward. 

            

2. The field lines around a system of two positive charges (q, q) give a vivid pictorial description of their mutual repulsion, while those around the configuration of two equal and opposite charges (q, –q), a dipole, show clearly the mutual attraction between the charges.

3. Field lines start from positive charges and end at negative charges. If there is a single charge, they may start or end at infinity.

4. In a charge-free region, electric field lines can be taken to be continuous curves without any breaks.

5.Two field lines can never cross each other. (If they did, the field at the point of intersection will not have a unique direction, which is absurd.)

6. Electrostatic field lines do not form any closed loops. This follows from the conservative nature of electric field.

7. The number of lines per unit area, through a plane at right angles to the lines, is proportional to the magnitude of E. This means that, where the lines of force are close together, E is strong and where they are far apart, E is weak.

8. Each unit positive charge gives rise to 1/εo lines of force in free space. Hence number of lines of force originating from a point charge q is N = q/εo in free space.