I keep getting “Path difference & fringes” questions wrong in Wave Optics. What's the trap?
mixing up the conditions for bright and dark fringes.
The usual trap: mixing up the conditions for bright and dark fringes. How to avoid it: path diff = nλ → bright; (n+½)λ → dark. Go back to the definition — bright fringes form where the path difference is a whole number of wavelengths, dark where it's an odd number of half-wavelengths.
Key point
Path difference & fringes
Common mistake
mixing up the conditions for bright and dark fringes.
Memory tip
path diff = nλ → bright; (n+½)λ → dark.
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