Electric field lines are these imaginary lines or curves we draw to help us visualize an electric field. Most fields are 3D in nature, but we usually draw the field lines in one plane or cross section only. The resulting diagrams are called the field maps or field patterns.
For example, we get a pretty good idea of the field resulting from two positive point charges from the field map above. Despite their simplicity, field maps are surprisingly expressive
- The tangent at any point of the field line is the direction of the electric field at that point.
- The density of the field lines conveys the magnitude of the field strength. Where the field lines are closely packed, the field strength is strong. Where the field lines are sparse, the field strength is weak.
Sometimes we are asked to draw the field pattern ourselves. Here are some helpful tips:
- Positive charges must have field lines starting from them.
- Negative charges must have field lines ending at them.
- The number of lines starting from or ending at charges should be proportional to the magnitude of the charges.
- Field lines can also start from or end at infinity.
- Field lines must not intersect (since the electric field cannot have two directions at one point).