Single-Slit Diffraction

When monochromatic light passes through a single slit of width a, it spreads out and produces a diffraction pattern on a distant screen.

The pattern consists of a bright central maximum flanked by alternating dark minima and weaker secondary maxima.

Minima occur where a sin θ = nλ (n = ±1, ±2, ...). NOT n = 0 — that's the central max.

The central maximum is twice as wide as any secondary maximum. Its angular half-width is λ/a.

Intensity envelope: I(θ) = I₀(sin α / α)², where α = πa sin θ / λ. Secondary maxima approximately at α = ±1.43π, ±2.46π, ...

First secondary max ≈ 4.5% of central max. Diffraction is more pronounced when a is comparable to λ.

Fraunhofer diffraction = far-field (source and screen at infinity). Fresnel diffraction = near-field. JEE assumes Fraunhofer.