🎇 Single-Slit Diffraction
📖 The Physics
Waves don't just travel in straight lines — they bend around obstacles and spread out after squeezing through a gap. When light passes through a single narrow slit, every point in the slit acts as a tiny wavelet, and these wavelets interfere.
The result is a broad central maximum with dimmer fringes on each side. This spreading is diffraction, and it only shows up clearly when the slit is comparable to the wavelength.
Dark fringes (minima): a·sinθ = m·λ (m = 1, 2, 3 …)
First minimum on screen: y₁ = λ·L / a
Make the slit narrower and the pattern spreads out wider — a smaller slit diffracts more. A longer wavelength (toward red) also widens it. The central bright band is always twice as wide as the others.
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