What is the role of the phase change upon reflection in thin film interference?

What is the role of the phase change upon reflection in thin film interference?

Step 1: Understand that thin film interference happens when light waves reflect off different surfaces of a thin film, like soap bubbles or oil slicks.
Step 2: Know that when light hits a boundary between two materials, some of it reflects back and some of it passes through.
Step 3: Recognize that if light reflects off a surface that has a higher refractive index (like air to water), it undergoes a phase change of π (which is equivalent to half a wavelength).
Step 4: This phase change means that the reflected light wave is shifted, which can either enhance or cancel out the light waves when they combine.
Step 5: The combination of these waves creates an interference pattern, which is why we see colors in thin films.

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