Final answer:
The distance between the top and bottom of the beam dictates the interference pattern produced when light passes through a narrow slit.
Step-by-step explanation:
The distance between the top of the beam and the bottom of the beam dictates the interference pattern produced when light passes through a narrow slit. When light passes through a narrow slit, it diffracts and creates a pattern of dark and bright regions on a screen. The distance between the top and bottom of the slit determines the angle at which the destructive interference occurs, resulting in the dark regions.