Representing Electric Fields
- The direction of electric fields is represented by electric field lines
Radial Fields
- A radial field spreads uniformly to or from the charge in all directions
- 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
The Field Lines Around Positive and Negative Point Charges
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
Uniform Electric Field
- 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
Field Lines in an Electric Field
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
Non-Uniform Electric Field
- 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
Field Lines in a Non-Uniform Electric Field
A non-uniform E field has lines not spaced equally apart. Denser regions of the field have field lines closer together and less dense regions further apart
Worked example
Sketch the electric field lines between the two point charges in the diagram below.
Answer:
- 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
Always add arrows to the field lines! The lines must also touch the surface of the source charge or plates.