Physics I / Wave Optics: Interference and Diffraction
Practice question · Multiple choice

In a double-slit experiment you make the two slits closer together. What happens to the bright fringes on the screen?

Hints
  1. Fringe condition: dsinθ=mλd\sin\theta = m\lambda. If dd shrinks, what must sinθ\sin\theta do to keep the equation true?
  2. Smaller dd → larger angles for the same order mm: the pattern inflates.
Show the answer

A. They spread farther apart

Why

The geometry is reciprocal: tighter slits throw a wider pattern (sinθ=mλ/d\sin\theta = m\lambda/d). This inverse relationship is the heart of diffraction, and the reason small things are hard to see with light: the finer the detail, the wider the light spreads.

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