The distance between the slits (often called slit separation) in Young’s double-slit experiment directly affects the interference pattern in these ways:
- Fringe spacing (fringe width):
- Increasing the slit separation makes the fringes closer together (fringe width decreases).
- Decreasing the slit separation causes the fringes to spread farther apart (fringe width increases).
- Number of fringes visible:
- Larger slit separation results in more fringes fitting within a given length on the screen, but they may become harder to resolve because they’re closer.
- Smaller slit separation means fewer fringes appear, but each fringe is wider and easier to observe.
- Sharpness of fringes:
If slits are very close, fringes are broad and easily visible; if too far apart, the fringes become very narrow and may blur.
Why this happens:
The fringe width is inversely proportional to the slit separation because the path difference between the two waves changes more rapidly when the slits are farther apart, creating more closely spaced interference bands.
In summary, the slit separation controls the spacing and number of interference fringes, influencing how the pattern appears on the screen.