Angular Width of a Principal Maximum consider N evenly spaced narrow slits. Use the small-angle approximation sin θ = θ (for θ in radians) to prove the following: For an intensity maximum that occurs at an angle θ, the intensity minima immediately adjacent to Ibis maximum are at angles θ + λ/Nd and o - A/Nd, so that the angular width of the principal maximum is 2λ/Nd. This is proportional to l/N, as we concluded in Section 36.4 on the basis of energy conservation.