A thin prism (A = 5°) is made of flint glass with n_red = 1.62 and n_violet = 1.66. (a) Find the deviation for red and violet. (b) Find the angular width of the spectrum. (c) Compare with crown glass (n_r = 1.51, n_v = 1.53). Step 1: δ_r ≈ (n_r − 1)A = 0.62 × 5° = 3.10°. δ_v ≈ 0.66 × 5° = 3.30°. Step 2: Spectrum width Δδ = δ_v − δ_r ≈ (n_v − n_r)A = 0.04 × 5° = 0.20°. Small — which is why spectrometers use large prisms or gratings. Step 3: Crown: δ_r = 0.51×5 = 2.55°, δ_v = 0.53×5 = 2.65°, Δδ = 0.10° — half the spread of flint. Dispersive powers: flint ω = 0.04/0.64 ≈ 1/16... using n_yellow ≈ 1.64: ω = (1.66−1.62)/(1.64−1) = 0.0625. Crown: (1.53−1.51)/(1.52−1) ≈ 0.038. Flint disperses ~1.6× more per unit bending — the reason flint–crown doublets can cancel colour while keeping power.