Single slit diffraction

Intermediate

Central maximum with decreasing side peaks.

Key relationa sinθ = mλ

Light through a slit of width a gives a central maximum with width 2λD/a and minima at a sinθ = mλ. A narrower slit gives a broader pattern.

Worked example

a = 0.1 mm, λ = 600 nm, D = 1 m: central width 12 mm.

Common mistake

Bright fringes outside the central are much dimmer.

In more detail

Single-slit diffraction produces a central bright maximum with weaker side maxima. The first minimum is at sin θ = λ/a, where a is the slit width.

Diffraction limits how small details a telescope or microscope can resolve.
Narrow slits are used in spectrometers to produce diffraction patterns.
A laser beam passing through a narrow slit spreads out, which shows single-slit diffraction.

Why does the central maximum get wider for narrower slits?

Because diffraction spreads the light more when the slit is smaller.

Is single-slit diffraction interference?

It can be viewed as interference between wavelets from different parts of the slit.

Why does a narrower slit spread the light more?

The diffraction angle grows as the slit width shrinks, so narrow slits produce wider spreads.