Key formulae — Electromagnetism

Summary of electromagnetism formulae (ch. 13–15, 17–19). Derivations and limits of validity are in the respective chapters.

Coulomb’s law $F = k\,\frac{q_1 q_2}{r^2}$

Field and potential (point charge) $E = k\,\frac{Q}{r^2} \qquad V = k\,\frac{Q}{r}$

Capacitor $C = \frac{Q}{V} \qquad C = \frac{\varepsilon_0 A}{d}\ \text{(piano)} \qquad E_C = \tfrac12 C V^2$

Ohm’s law and power $V = Ri \qquad P = Vi$

Resistors in series and parallel $R_s = R_1 + R_2 \qquad \frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2}$

Lorentz force $\pq{F} = q\,\pq{v}\times\pq{B}$

Magnetic field of sources $B = \frac{\mu_0 i}{2\pi r}\ \text{(filo)} \qquad B = \frac{\mu_0 i N}{\ell}\ \text{(solenoide)}$

Faraday-Neumann-Lenz law

$\Gamma_E = -\ddt{\Phi_B}$

Maxwell’s equations in integral form: see the formula sheet in ch. 19.

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Topics: Electrostatics · Electric circuits · Magnetism · Electromagnetic induction