• Tags: single-slit, diffraction, central-maximum
• Difficulty: Moderate

A slit of width a produces a diffraction pattern: minima at a sinθ = nλ (n = ±1, ±2, ...). The central maximum has angular width 2λ/a and linear width 2λD/a on the screen at distance D. Secondary maxima are approximately at a sinθ ≈ (2n+1)λ/2 and are much dimmer than the central maximum. Intensity ratios: central : 1st secondary : 2nd secondary ≈ 1 : 0.045 : 0.016. The central maximum contains about 84% of the total light energy. Important: as slit width a increases, the central maximum narrows (less diffraction). As a → ∞, the pattern approaches geometric shadow. As a → λ, the central maximum spreads to fill the entire screen.