Magnetism and magnetic effects of electric current — Formula Sheet

Magnetic dipole moment p_m = q_m × 2l, where q_m is pole strength and 2l is magnetic length. Direction: south to north pole.

Magnetic length is always less than geometrical length. Ratio = 5/6 ≈ 0.833.

Magnetic field B = F/q_m. Unit: N A⁻¹ m⁻¹ (or Tesla).

Torque

τ = p_m × B sinθ (in magnitude), Vector form: τ⃗ = p⃗_m × B⃗.

Potential energy

U = −p_m B cosθ = −p⃗_m · B⃗ (reference: θ = 90°).