SACE Stage 2 Physics — Light & Atoms 3.1

Diffraction Grating

N evenly-spaced slits, all illuminated in step by a plane wave. At angles where every adjacent pair shares a path difference of mλ the waves all conspire — a sharp principal maximum. The condition d sin θ = mλ is unchanged from the double slit; what changes is how cleanly each maximum stands out as N grows, and — with white light — that each order spreads into a spectrum.