Revise: Interference and Diffraction of Light
Huygens' principle, interference and diffraction of light, and how a diffraction grating splits it into a spectrum.
Every point on a wavefront is a source of secondary wavelets.
Explains why waves bend around obstacles and through gaps.
Δy = λL/d — fringe spacing in a double-slit pattern.
λ=600nm,d=0.5mm,L=2m → Δy=2.4mm.
d sinθ = mλ — sharp bright bands from many slits.
600 lines/mm, m=2, λ=550nm → θ≈41.3°.
The new wavefront is the envelope of all the wavelets.
Light diffracts too, just less noticeably than sound.
Direct evidence that light behaves as a wave.
Young's 1801 double-slit experiment.
Sets a fundamental resolution limit for any optical instrument.
Caused by wavelets from different parts of the slit canceling.
A diffraction order does not exist if mλ/d>1.
A CD's rainbow reflection is a diffraction grating effect.