Electric Field Lines (SL IB Physics)

• 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

Electric Fields Around Point Charges

• 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 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 and 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 represented by the spacing of the field lines:
  • A stronger field is represented by the field lines which are closer together
  • A weaker field is represented by the field lines which are  further apart

Electric Field Lines Between Two Parallel Plates

• The electric field lines are directed from the positive to the negative plate

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

• A radial field is considered a non-uniform field
  • Electric field strength E varies with distance from a charged particle

• The density of electric field lines determines the strength of an electric field
  • Regions where the electric field lines are closer together, mean the electric field is stronger
  • Regions where the field lines are further apart mean the electric field is weaker

Example of Different Field Line Density

The field lines on the left-hand side are much closer together than the field lines on the right-hand side. This means that the electric field is stronger on the left than it is on the right.

 Density of Field Lines Around Point Charges

• The stronger an electric point charge then the stronger the electric field around it and the higher the density of its field lines

Electric field strength A > Electric Field Strength B > Electric Field Strength C

So, Magnitude of Charge A > Magnitude of Charge B > Magnitude of Charge C