Wave optics — light interferes with itself

Rays explained mirrors and lenses; they cannot explain why two slits paint stripes or why a soap bubble has colours. Here light is a wave: every point on a wavefront re-emits, path differences of whole wavelengths add up and half wavelengths cancel. One number rules the chapter — the path difference Δ, counted in wavelengths.

✋ drag P on every screen 🎨 colours here are true wavelength colours

01 — every point is a new source

Huygens’ wavelets — Snell for free

Every point a wavefront touches becomes a tiny source of secondary wavelets; the new front is their common envelope. When the front hits a slower medium, the wavelets there grow more slowly — the envelope tilts, and the whole beam bends. Refraction is not a rule; it is arithmetic.

show:

incidence i{{ huyItxt }}

λ₂ / λ₁{{ huyLamTxt }}

v₂{{ huyVtxt }}

sin isin r = v₁v₂ = n

i = r — wavelets in the same medium grow at the same speed, so the envelope leaves at the angle it arrived

angle of incidence i{{ huyItxt }}

index n of medium 2{{ huyNtxt }}

Frequency never changes at a boundary — the glass cannot swallow crests. So v = fλ forces λ to shrink by n: watch the fronts bunch up below the surface.

↑ Part of Vedatom Physics | built by Dr. Tejaswi Katravulapally |

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