Revise: Electric Field
Coulomb's law, electric field intensity, lines of force, charge distribution, electric potential and potential difference, and equipotential surfaces.
F = kq₁q₂/r²; like charges repel, opposite attract, force follows inverse-square law.
3µC and 2µC charges 0.5 m apart attract with ≈0.216 N.
E = F/q defines field strength independent of the test charge used.
0.4 N on a 2µC charge gives E = 2×10⁵ N/C.
V = kQ/r; potential difference (voltage) drives current in circuits.
5µC at 0.3 m gives V ≈ 1.5×10⁵ V.
V = Ed for the uniform field between parallel plates.
240 V across a 0.02 m gap gives E = 12,000 V/m.
Field lines point from + to −; closer lines mean a stronger field.
Evenly spaced parallel lines represent a uniform field between plates.
Charge concentrates at sharply curved points on a conductor.
Lightning rods use sharp points to concentrate charge.
Equipotential surfaces are always perpendicular to field lines; no work along them.
A bird on one power line is safe — no potential difference across its body.
The Earth's potential is defined as zero — a stable, universal reference (ground).
Grounding an appliance provides a safe path to Earth's zero-potential reference.