Chad provides a lesson on Thin Film Interference. When a thin film of a liquid is in between two other mediums, the reflected rays at the top and bottom surface of the film have a chance to undergo either constructive or destructive interference depending upon the thickness of the film and the wavelength of the light. For a given film thickness, some wavelengths will experience constructive interference while others destructive interference resulting in certain colors of white light becoming visible in the reflected rays. Chad derives and presents the equations for the conditions of both constructive and destructive interference. One additional factor to consider is that when light is moving from a medium with a lower index of refraction to one of a higher index of refraction the reflected ray will be inverted, and this must also be accounted for. If there is a relative phase shift between the reflected rays at the top and bottom surfaces of the thin film, then the conditions for constructive and destructive interference will switch to the exact opposite. Ultimately, two sets of equations are presented, one set when there is no relative phase shift between the reflected rays, and one set when there is. The lesson is concluded with the solving of a Thin Film Interference Practice Problem.

00:00 Lesson Introduction
00:51 Introduction to Thin Film Interference
05:37 Inversion of Some Reflected Light Waves
06:44 Thin Film Interference Without a Relative Phase Shift
10:26 Thin Film Interference With a Relative Phase Shift
15:28 Thin Film Interference Practice Problem

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