Figure 8: Analysis of diffraction experiment with slit of finite width
Figure 8 shows how we can compute the intensity
pattern for a slit of finite width a (no longer infinitesimal
compared to the wavelength) by using our result for N slits. The
idea is simple. If we made a diffraction grating with N small slits
spaced very closely apart at distance d=a/N, and kept adding more
little slits, eventually we end up removing all of the grating,
leaving just a single slit of width 
. The
special term diffraction is generally used to describe
interference patterns formed by finite openings. The underlying
physical principle, however, remains interference.