When light reflects from a thin film, whether or not a phase shift occurs at one or both of the reflecting surfaces, the single characteristic of the fringes that is affected by this potential change is
A) their separation.
B) their position.
C) their sense (dark followed by bright, or vice versa).
D) None of the previous responses is valid.

Question

Quizplus · Accepted Answer

The phase shift that occurs when light reflects off a thin film can invert the order of the interference fringes, changing their sense (i.e., from dark followed by bright to bright followed by dark, or vice versa). This is because the phase shift can either add or subtract half a wavelength to the path difference, depending on whether the reflection occurs at a medium of higher or lower refractive index, thus affecting the constructive and destructive interference pattern.

When Light Reflects from a Thin Film, Whether or Not