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. Dipole moment: p = q × 2a = 7 × 10⁻⁶ × 3 × 10⁻³ = 2.1 × 10⁻⁸ C m . Torque: tau = p E sin θ = 2.1 × 10⁻⁸ × 4 × 10⁴ × sin 60° = 8.4 × 10⁻⁴ × (√(3)/2) = 7.28 × 10⁻⁴ N