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Electric Lines of Force

The electric field in a region is represented by continuous lines (also called lines of force).
Properties of electric lines of force
  1. Electric field lines come out of positive charge and go into the negative charge.
  2. Tangent to the field line at any point gives the direction of the field at that point (Fig. 7).
  3. Field lines never intersect each other.
Fig. 7
  1. Field lines are always normal to conducting surface.
  2. Field lines do not exist inside a conductor.
Fig. 8
  1. The electric field lines never form closed loops. (While magnetic lines of forces form closed loop)
  2. The number of lines originating or terminating on a charge is proportional to the magnitude of charge i.e., |Q| ∝ number of lines. In Fig. 9, |QA| >|QB|.
Fig. 9
  1. If the lines of forces are equidistant and parallel straight lines the field is uniform and if either lines of force are not equidistant or straight line or both the field will be non uniform, also the density of field lines is proportional to the strength of the electric field.
Fig. 10
Some Important Notes
  • Unit field, i.e., 1N/C is defined arbitrarily as corresponding to unit density of lines of force.
  • Number of lines originating from a unit charge is 1/ε0.
  • It is a common misconception that the path traced by a positive test charge is a field line but actually the path traced by a unit positive test charge represents a field full line only when it moves along a straight line.

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