An electric dipole of moment p is placed in a uniform field E. The work done to rotate it from the orientation θ = 0 (aligned with the field) to θ = 180° is

1. PE in a uniform field: U(θ) = −p·E = −pE cos θ. 2. W = ΔU = U(180°) − U(0°) = (+pE) − (−pE) = 2pE. 3. The dipole goes from the most stable to the least stable orientation; work is positive on the system. _Source: syllabus Physics Part I, Ch 2 §2.8.3_