When one of the slits in Young’s double-slit experiment is blocked:
- Interference pattern disappears:
The characteristic bright and dark fringes formed by interference are no longer seen. - Single-slit diffraction occurs:
Only the pattern due to diffraction from a single slit remains, which is usually a broad central maximum with weaker side bands. - No superposition:
Since only one wavefront passes through, there is no overlap of two coherent light waves to produce constructive or destructive interference. - Reduced brightness pattern:
The light intensity on the screen is generally lower because only half the original light passes through. - Loss of fringe information:
Blocking one slit removes the path difference responsible for the fringe positions, so detailed interference-based measurements become impossible.
In short, with one slit blocked, the experiment behaves like a single-slit diffraction setup and does not demonstrate the wave interference principle.