**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.

Thu Sep 13 15:26:14 EDT 2001