Dipole: two equal and opposite charges +q, -q separated by 2a. Dipole moment: p = q(2a), directed from -q to +q. SI unit: C m. For r >> a: Axial point (on the dipole axis): $E_{axial}$ = 2kp/$r^3$ (along p). Equatorial point (perpendicular bisector): $E_{eq}$ = $\frac{kp}{r}$^3 (opposite to p). General point at angle theta from axis: E = (kp/$r^3$)sqrt(1 + 3$cos^2$(theta)). In a uniform external field E: Torque tau = p x E, |tau| = pEsin(theta). Potential energy U = -p.E = -pE*cos(theta). Stable equilibrium: theta = 0 (p parallel to E, U = -pE minimum). Unstable equilibrium: theta = pi (U = +pE maximum). Work to rotate from $theta_1$ to $theta_2$: W = pE(cos($theta_1$) - cos($theta_2$)).