Divide by the Wavelength First

You'll learnwhat decides whether two paths reinforce or cancel, how the bright orders are numbered, and why a grating throws thin rainbow lines out to angles where the usual shortcut fails.

Two slits light one screen and the light lands in stripes. The extra distance one route travels decides everything, once it is divided by the wavelength. Twelve short steps; press Next for each one.

12 STEPS · 6 QUICK CHECKS · DIVIDE BY λ FIRST · THE CENTRE IS m = 0 · CHECK θ IS SMALL · v2

divide the path difference by λ · the centre is order zero · check θ first

Before you start

What you're looking at

Two slits and a screen, with the two routes light takes to one point and the extra distance one of them travels marked in blue.

The question

Why does light plus light make dark stripes, and which stripe is which order?

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