How do interference fringes change when the distance between slits is changed?

When the distance between the slits in a double-slit experiment is changed, the interference fringes also change in appearance:

1. If the slit separation increases:
   • The fringes get closer together (fringe width decreases).
   • This happens because the angle for constructive interference becomes smaller, so bright spots appear more closely spaced on the screen.
2. If the slit separation decreases:
   • The fringes spread farther apart (fringe width increases).
   • Light waves from the slits interfere constructively at wider angles, so the fringes are more widely spaced.

In summary, the fringe width is inversely proportional to the distance between the slits. More separation means narrower spacing of fringes, and less separation means wider spacing.