Practice question

**Electric dipole** consists of charges +q and -q separated by 2a, dipole moment p = q·2a, vector from negative to positive, unit C·m. In uniform field E, torque τ = p × E, magnitude τ = p E sinθ, tending to align p with E, potential energy U = -p·E = -p E cosθ. Torque: tau = p E sin θ . tau = 5 × 10⁻⁹ × 4 × 10⁴ × sin 60° = 20 × 10⁻⁵ × (√(3)/2) = 1.732 × 10⁻⁴ N m . Substituting values gives 1.73 × 10⁻⁴ N m, which matches expected magnitude for this electrostatic configuration, confirming Coulomb's