AQA A Level Physics

Revision Notes

7.4.2 Electric Field Lines

Representing Electric Fields

  • The direction of electric fields is represented by electric field lines
  • Electric field lines are directed from positive to negative
    • Therefore, the field lines must be pointed away from the positive charge and towards the negative charge
  • A radial field spreads uniformly to or from the charge in all directions
    • e.g. the field around a point charge or sphere
  • Around a point charge, the electric field lines are directly radially inwards or outwards:
    • If the charge is positive (+), the field lines are radially outwards
    • If the charge is negative (-), the field lines are radially inwards

Radial E field lines, downloadable AS & A Level Physics revision notes

Electric field lines point away from a positive charge and point towards a negative charge

  • This shares many similarities to radial gravitational field lines around a point mass
  • Since gravity is only an attractive force, the field lines will look similar to the negative point charge, whilst electric field lines can be in either direction
  • A uniform electric field has the same electric field strength throughout the field
    • For example, the field between oppositely charged parallel plates
  • This is represented by equally spaced field lines
    • This shares many similarities to uniform gravitational field lines on the surface of a planet
  • A non-uniform electric field has varying electric field strength throughout
  • The strength of an electric field is determined by the spacing of the field lines:
    • A stronger field is represented by the field lines closer together
    • A weaker field is represented by the field lines further apart

Parallel E field lines, downloadable AS & A Level Physics revision notes

The electric field between two parallel plates is directed from the positive to the negative plate. A uniform E field has equally spaced field lines

  • The electric field lines are directed from the positive to the negative plate
  • A radial field is considered a non-uniform field
    • So, the electric field strength E is different depending on how far you are from a charged particle

Worked Example

Sketch the electric field lines between the two point charges in the diagram below.

WE Representing Electric Fields question diagram, downloadable AS & A Level Physics revision notes

  • Electric field lines around point charges are radially outwards for positive charges and radially inwards for negative charges
  • The field lines must be drawn with arrows from the positive charge to the negative charge

Representing_Electric_Fields_Worked_example_solution_diagram, downloadable AS & A Level Physics revision notes

Exam Tip

Always label the arrows on the field lines! The lines must also touch the surface of the source charge or plates.

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