CIE A Level Physics复习笔记18.1.2 Electric Field Lines

• 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

• 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

• 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.

• 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

Exam Tip