In Young's double-slit experiment, what happens to the fringes if I move the slits closer together?
Fringe width is β = λD/d, so it's inversely proportional to the slit separation d.
Fringe width is β = λD/d, so it's inversely proportional to the slit separation d. Bringing the slits closer (smaller d) makes the fringes wider and more spread out; pushing them apart squeezes the fringes together. Widening the screen distance D or using longer-wavelength (redder) light also widens the fringes.
Key point
β = λD/d — smaller slit separation d gives wider fringes.
Common mistake
thinking closer slits crowd the fringes together.
Memory tip
fringe width ∝ λD/d: closer slits (small d) → wider fringes.
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