Coulomb's law

Force between point charges in a vacuum:
\(F = \dfrac{1}{4πε_0}\dfrac{Q_1Q_2}{r^2} \)

Permittivity of free space, ε₀

Appreciation that air can be treated as a vacuum when calculating force between charges.

For a charged sphere, charge may be considered to be at the centre.

Comparison of magnitude of gravitational and electrostatic forces between subatomic particles.

Electric field strength

Representation of electric fields by electric field lines.

Electric field strength.

E as force per unit charge defined by \(E = \dfrac{F}{Q} \)

Magnitude of E in a uniform field given by \(E = \dfrac{V}{d} \)

Derivation from work done moving charge between plates: \(Fd = QΔV \)

Trajectory of moving charged particle entering a uniform electric field initially at right angles.

Magnitude of E in a radial field given by \(E = \dfrac{1}{4πε_0}\dfrac{Q}{r^2} \)

Electric potential

Understanding of definition of absolute electric potential, including zero value at infinity, and of electric potential difference.

Work done in moving charge Q given by \(∆W = Q∆V \)

Equipotential surfaces.

No work done moving charge along an equipotential surface.

Magnitude of V in a radial field given by \(V = \dfrac{1}{4πε_0}\dfrac{Q}{r} \)

Graphical representations of variations of E and V with r.

V related to E by \(E = \dfrac{∆V}{∆r} \)

\(∆V\) from the area under graph of E against r.