Dear Friends, it is very important to discuss the concept of electric lines of force or commonly known as field lines also as these will become the foundation to understand the concept of electricity. Today we will discuss electric lines of forces and their properties:

Definition of Electric line of force:

An electric line of force is a path, straight or curved, such that tangent to it at any point gives the direction of electric field intensity at that point.

In Fig. 1, PQ is an electrostatic line of force. The tangent to the line at any point A gives the direction of electric intensity  EA at A. Similarly, tangent to PQ at B gives the direction of EB, (see Figure)

Let us discuss the direction of electric field lines for different types of charges:

1. For a single positive point charge,   these lines are directed radially outwards.

The lines of force extend to infinity, (Fig. 2)

2. For a single negative point charge, these lines are directed radially inwards. (Fig. 3).

3. For pairs of equal and opposite charges,   lines of force are shown in Fig. 4.

Above is the definition of electric field lines and their directions for different types of charges. One can also understand magnetic flux similarly.

Properties Of Electric Lines Of Force :

1. Electric lines of force are discontinuous curves. They start from a positively charged body and end at a negatively charged body (Fig. 1.4). No electric lines of force exist inside the charged body.
2. Tangent to the line of force at any point gives the direction of electric intensity at that point.
3. No two electric lines of force can intersect each other. This is because at the point of intersection P, we can draw two tangents PA and PB to the two lines of force. This   would   mean  two   directions of electric intensity   at   the   same  point,   which is not possible. Hence no two lines of force can cross each other.

Above are the main properties of electric lines of force with the reason why no two electric lines of force can cross each other.

Following is our youtube video on Electric lines of force: