Electric fields · Year 13
An electric field is the region around a charge where other charges feel a force. Field strength E is the force on each coulomb of charge placed there. Fields can be drawn with lines: radial around a point charge, and uniform (parallel and evenly spaced) between two charged plates – the arrangement used in inkjet printers, cathode-ray tubes and particle accelerators.
Key facts
- E = F ÷ q (N/C), so F = qE.
- Point charge: E = kQ ÷ r², with k = 9.0 × 10⁹ N m²/C².
- Between parallel plates: E = V ÷ d (V/m, the same as N/C).
- Field lines point from + to −, never cross, and are closer where the field is stronger.
- Work done on a charge moved through a p.d.: W = qV; an electron accelerated through V gains eV of kinetic energy.
- Fields from several charges add as vectors.