How does the angle of incidence affect the interference fringes?

The angle of incidence affects the interference fringes in Young’s double-slit experiment by altering the symmetry and spacing of the fringe pattern:

1. Normal incidence (zero angle):
   When light strikes the slits perpendicularly, the interference fringes are evenly spaced and centered directly opposite the midpoint between the slits. The bright and dark bands form a symmetrical pattern.
2. Oblique incidence (non-zero angle):
   If the light hits the slits at an angle, the path difference between the two beams changes. This causes:
   • A shift in the central maximum away from the midpoint.
   • The entire fringe pattern becomes asymmetric.
   • The spacing between fringes may appear slightly altered, especially if the angle is large.
3. Effect on fringe position:
   The angle modifies the path difference for each point on the screen, affecting where constructive and destructive interference occurs. This means the interference pattern is no longer centered where it would be under normal incidence.

In summary, the angle of incidence shifts the position of the fringes and can distort their symmetry, but the basic interference effect still occurs as long as the light remains coherent.