Every charge produces its own electric field, and other charges experience the electric force in the vicinity of that charge. This force could be either attractive or repulsive, depending on the nature of the charges.

We cannot ‘see’ electric fields with our naked eyes. These electric fields can be pictorially represented by the ‘electric lines of forces’.

History:

Electric fields are everywhere, but we cannot ‘see’ them with our naked eyes. To visualise these electric fields, Michael Faraday, in the year 1837, introduced the concept of electric lines of forces. With the help of these lines, we can find the direction of the electric field and the direction of electric force at every point in space. The concept of representing vector field lines with the help of lines of force is so fundamental that it helps a lot while studying the complex system. This concept of representing any vector field by drawing lines on paper is often used to study gravitation, fluid dynamics, aerodynamics, electrostatic and magnetostatic.

Definition:

Electric lines of forces are imaginary lines drawn in space such that the tangent drawn at any point on the line gives the direction of the electric field and the direction of electric force.

The diagram below consists of a positive and a negative charge kept near each other. We can find the direction of the electric field at points A and B by drawing tangents at the respective points as shown: 

Electric lines of force due to charges: 

The diagram below shows the electric lines of force for positive and negative charges:

1. For positive charge, the electric lines of forces are shown as directed away from the charge. There is an infinite number of electric lines of force due to this charge. 
2. For negative charge, the lines of forces are shown as directed towards the charge. There is an infinite number of electric lines of force due to this charge. 
3. Each electric line of force is continuous and extended up to infinity. 

Electric lines of forces due to pair of positive and negative charge 

In this case, the lines emerge from the positive charge and end up at the negative charge. These lines could be curved as well as straight, but they never intersect or meet with each other. The diagram below shows the electric lines of force for the case. This diagram also represents the ‘attractive’ nature of force between these charges. This is because the lines that emerged from the positive charge and converged into the negative charge are in the same direction.         

Electric lines of force due to pair of like charges

In this case, the lines emerge from both positive charges and end up at infinity. These lines could be curved as well as straight, but they never intersect or meet with each other. The diagram below shows the electric lines of force for the case. This diagram also represents the ‘repulsive’ nature of force between these charges. This is because the lines that emerged out from positive charge and emerged out from positive charge are in the opposite direction.    

General characteristics 

1. Conventionally, the electric lines of force always emerge from a positive charge. These lines converge into a negative charge. 
2. Electric lines of force never intersect each other. The reason is that if two electric lines of force are intersecting, then that electric field has two different directions at a single point, which is impossible.
3. Electric lines of force don’t pass through the conducting media because the electric field inside a conducting material is always zero.
4. Electric field intensity at a point is directly proportional to the number of electric lines of force passing through the surface held perpendicular to its direction.
5. Electric lines of force are gathered together near a point where the electric field intensity is maximum. On the other hand, these lines are separated apart wherever the electric field intensity is minimum.
6. Electric lines of force due to static electric fields never form a closed loop.
7. Electric lines of force are always continuous. They never break in between.
8. The electric lines of force in the opposite direction of each other attract each other. At the same time, the lines in the same direction repel each other.

Conclusion 

Electric fields can be visualised with the help of the concept of ‘lines of force’. We have seen some characteristics and behaviour of these lines in different charge distributions.  The electric lines of force are taken as emerging from the positive charge and ending in the negative charge. This convention is followed by the scientific community.