Electric fields
An electric charge creates an electric field around it, and any other charge placed in that field feels a force proportional to the field strength there.
Practise this conceptEvery electric charge sets up a field in the space around it — an invisible influence that would push or pull on any other charge placed nearby, even before that other charge actually arrives. The field is a property of the source charge, existing whether or not anything is there to feel it.
Field strength falls off with distance from the source, so a charge placed closer to another charge feels a stronger push or pull than one placed farther away. Crucially, the field at a given point doesn't depend on the size of whatever test charge you use to probe it — a bigger test charge feels a bigger force, but the field itself, force divided by that test charge, comes out the same either way.
Field lines are a useful drawing convention for visualising all this: they point in the direction a small positive charge would be pushed, and where they bunch closer together, the field is stronger. They're a map of the field, not a set of tracks that a charge is somehow forced to follow.
Key ideas
Requires: Electric charge and current, Scalars and vectors
Unlocks: Magnetic fields
Formulas
| Symbol | Name | Unit |
|---|---|---|
| electric field | N/C (newton per coulomb) | |
| electric charge | C (coulomb) | |
| distance | m (metre) |
Common misconceptions
- Electric field lines show the actual path a charge will always follow.
- The electric field at a point depends on the size of the test charge placed there.
- Electric field strength does not depend on distance from the source charge.