Physics (AS & A Level) · May / June 2017 · Paper 13 · Question 28

Monochromatic light of wavelength λ is incident on two narrow slits S₁ and S₂, a small distance apart. A series of bright and dark fringes are observed on a screen a long distance away from the slits. The nth dark fringe from the central bright fringe is observed at point P on the screen. Which equation is correct for all positive values of n?

1. AS₂P – S₁P = nλ/2
2. BS₂P – S₁P = nλ
3. CS₂P – S₁P = (n – ½)λ
4. DS₂P – S₁P = (n + ½)λ

As printed in the paper