Electric Field Lines – Class 12 | Chapter – 1 | Physics Short Notes Series PDF for NEET & JEE

Electric Field Lines: Electric field lines are a graphical representation of the electric field at each point in space. They provide a visual representation of the direction and magnitude of the electric field and are often used to help understand the behavior of charged particles in an electric field.

Electric Field Lines

Electric field lines are usually drawn starting from positive charges and extending outward into the surrounding space. They can also be drawn starting from negative charges and extending inward. The field lines always point in the direction of the electric field, so the electric field at a point is given by the direction of the field line at that point. The strength of the electric field can be represented by the spacing of the field lines, with closer lines indicating a stronger field and farther lines indicating a weaker field.

It’s important to note that electric field lines are not physical objects and do not exist in space. They are a mathematical representation of the electric field, and their properties are determined by the distribution of charges in space. The concept of electric field lines is useful for visualizing and understanding the behavior of charged particles in an electric field, but it should not be taken as a literal representation of the electric field.

Properties of Electric Field Lines

The properties of electric field lines are determined by the distribution of charges in space and the behavior of charged particles in electric fields. The following are some of the key properties of electric field lines:

  • Direction: Electric field lines always point in the direction of the electric field at each point in space. The electric field at a point is given by the direction of the field line at that point.
  • Magnitude: The strength of the electric field at a point is proportional to the density of the electric field lines at that point. Closer lines indicate a stronger field, and farther lines indicate a weaker field.
  • Origin and Termination: Electric field lines originate from positive charges and terminate at negative charges. For a single isolated charge, the field lines extend indefinitely in all directions. For a distribution of charges, the field lines form closed loops that enclose the charges.
  • Continuity: Electric field lines are continuous and do not intersect or cross each other, except at charges where they originate or terminate.
  • Symmetry: Electric field lines are symmetric with respect to the distribution of charges. For example, if two charges of the same magnitude are placed symmetrically with respect to a point, the electric field lines at that point will be symmetrical with respect to the two charges.
  • Conserved Quantity: The total number of electric field lines originating from or terminating at a charge is proportional to the charge. This property is a manifestation of the conservation of charge, which states that the total amount of electric charge in a closed system remains constant.

Electric Field Lines Attraction and Repulsion

Electric field lines can indicate attraction or repulsion between charged particles based on their direction and relative orientation.

Attraction: Electric field lines pointing from a positive charge towards a negative charge indicate an attractive force between the two charges. In this case, the electric field lines are said to be converging.

Repulsion: Electric field lines pointing from a positive charge away from another positive charge, or from a negative charge away from another negative charge, indicate a repulsive force between the charges. In this case, the electric field lines are said to be diverging.

Rules for Drawing Electric Field Lines

There are several rules that are followed when drawing electric field lines to represent the electric field at each point in space. These rules include:

  • Field lines start from positive charges and end on negative charges.
  • The number of field lines originating from or ending on a charged particle is proportional to the magnitude of its charge.
  • The field lines never cross or intersect each other, except at charges where they originate or end.
  • The direction of the field line at a point indicates the direction of the electric field at that point.
  • The closer the field lines are to each other, the stronger the electric field. The farther apart the field lines are, the weaker the electric field.
  • The field lines are continuous and form closed loops around any charge distributions.
  • The field lines are symmetrical with respect to the distribution of charges, such that the field lines around two charges of the same magnitude and sign will be mirror images of each other.


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By Team Learning Mantras