What is Electric Field Line: Definition, Properties, Formulas & Notes

The electric field lines are either continuous or discontinuous curves which drawn tangential to the direction of the net force at a point charge (test subject with a very, very small charge). The electric field lines depict the directions of the flow of positive charge towards negative charge.

These lines are imaginary lines only used as a hypothetical concept to show the electric field around the charges. This visual representation method of the electric field direction and strength was invented by Faraday.

Why do we use electric field lines?

1. These lines help us represent the behaviour of electric fields.
2. We can know the behaviour of the interaction between the charges.
3. A key concept in determining the electric field direction and strength.
4. A key concept for competitive exams like JEE and NEET. These exams ask to find the electric field lines for a system charges.

Read More: NCERT Solutions 

The electric field lines are a key concept in the electric field and charge class 12 physics chapter 1. NCERT Textbooks have given a detailed version of the characteristics of the electric field lines. Check here the properties of electric field lines.

• It is assumed that these imaginary electric field lines always start from the positive charge and end at the negative charge. In other words, it means that if we place a positive charge in an electric field line, it will move towards the negative charge. This means the net flow of charge in the electric field is from +ve to -ve charge.
• The electric field lines never intersect each other. This happens because if these lines are allowed to intersect, there will be two directions of electric field lines. It is not possible that the electric field at a point has two directions.

• The electric field lines are always perpendicular to the surface of the charge. 

• The density of electric field lines at any region depicts the intensity or strength of the electric field. The higher the number of lines present/ the closer the field lines are, the stronger the electric field will be.
• The exact direction of the electric field at a point is given by the tangent drawn to the field line.
• The length of the tangent drawn represents the net electric field intensity.
• For a single positive charge, the field lines end at infinity, and for a single negative charge, the field lines start at infinity.
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 The electric field lines move away from the positive charge and move towards the negative charge. This behaviour of the electric field is represented through the pattern and direction of field lines between charged particles. 

Repulsion: 

1. Charge involved: Two Positive charges and two negative charges (like charges).
2. The field line starts from positive charges and goes outward.
3. The line moves outwards, indicating repulsion
4. No lines connect them; charges push each other away.
5. Electric field lines appear to bend or repel from the region between them.

Attraction: 

1. Charge involved: Positive and negative charges
2. The field line starts from a positive charge and ends on a negative charge.
3. Line curves toward each other, indicating attraction

Keep below points given below in mind while drawing the electric field lines for the given charge or system of charges.

• The field line starts from a positive charge and ends on a negative charge or an infinite 
• The Field lines should never intersect each other.
• The tangent on an electric field line at any point gives the direction of the electric field at that point.
• The electric field is stronger when the lines are closer
• Field lines never form close loops
• The path of the positive test charge, followed by the electric field, is shown by field lines.

Class 12 Physics Chapter 1 discusses electric field lines in detail.  We can get a visual representation of the electric field direction and strength. Check below the important focus points for exams like JEE Main below;

• For a single positive charge, lines radiate outward and converge inward for a negative charge. In a dipole, lines curve from positive charges to negative charges.
• For a point charge, the electric field density $E\propto 1/r^2$ . 
• According to the Gauss law, the flux is proportional to the number of lines crossing a surface. This is a reason why there is zero field inside conductors.

 Here is the complete study material for Class 12 CBSE exams based on NCERT Textbooks.