Physics 312 Lecture: "Interference in the Double-Slit Experiment." Apr 24, 1998

Light from a single source which passes through two slits can interfere with itself
The result is a pattern of bright bands and dark bands on some surface far from the slit mask
Bright bands occur where waves from the two slits reach the surface in phase with each other; dark bands occur where the waves are out of phase

The general formula is

          d sin(theta) = m         lambda         constructive interference

          d sin(theta) = (m + 1/2) lambda         destructive interference

The central bright spot is brightest, but the maxima near it are only slightly less bright
Light which partially passes through and partially reflects off a thin film of material can also interfere with itself
If a light ray in one substance reflects off an interface to a material with a higher index of refraction, its phase is reversed
If a ray which reflects off the front surface a film, and a ray which reflects off the back surface of a film, recombine in phase, one sees the reflected light; if they recombine out of phase, no reflection appears
The reflection from a thin film can depend strongly on wavelength

This lecture discusses material in Chapter 37 of Serway.