Electric Fields (CIE IGCSE Physics)

Extended tier only

• An electric field is defined as:

A region of space in which an electric charge experiences a force

• The direction of an electric field at a point is defined as:

The direction of the force on a positive charge at that point

• Charged objects create electric fields around themselves
  • This is similar to how magnets create magnetic fields

• An electric field is a vector quantity as it has both magnitude (strength) and direction

Extended tier only

• Electric field lines are
  • used to represent the direction and magnitude of an electric field
  • always directed from the positive charge to the negative charge

Electric field around a point charge

• 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

Electric field lines around positive and negative point charges

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

Electric field around a charged conducting sphere

• The field lines around a charged conducting sphere are similar to that of a point charge
  • This is because the charges on the surface of the sphere will be evenly distributed
  • The charges are the same, so they repel
  • The surface is conducting, allowing them to move

• Field lines are always perpendicular (at right angles) to the surface of a conducting sphere

Electric field lines around a positively charged sphere

The electric field pattern around a conducting can be demonstrated using a Van der Graaff generator

Electric field between two parallel plates

• The electric field between two parallel plates is a uniform electric field
• The field lines are:
  • directed from the positive to the negative plate
  • parallel
  • straight lines

Electric field lines between two oppositely charged parallel plates

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