CIE A Level Physics (9702) exams from 2022

Revision Notes

18.1.2 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
  • 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 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 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
  • 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

Representing_Electric_Fields_Worked_Example_-_Drawing_Electric_Field_Lines_Question, 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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Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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