A soap film has an index of refraction n=1.50. The film is...

A soap film has an index of refraction $n=1.50$. The film is viewed in transmitted light. (a) At a spot where the film thickness is $910.0 \mathrm{~nm}$, which wavelengths are weakest in the transmitted light? (b) Which wavelengths are strongest in transmitted light?

Key Concepts

Optical Path Difference

This refers to the effective difference in travel distance between two light rays as they pass through a medium. In thin film interference, the optical path difference is determined by the film’s thickness and its index of refraction, which affects the phase relationship between the interfering waves.

Phase Change on Reflection

When light reflects from a medium with a higher refractive index than the one it is coming from, it undergoes a phase shift of ? (equivalent to half a wavelength). This phase change is crucial in determining whether the interference between multiple light waves will be constructive or destructive.

Thin Film Interference

This is the phenomenon where light waves reflected from the top and bottom surfaces of a thin film interfere with one another. The interference can be constructive or destructive depending on the optical path difference and phase shifts, leading to colors that vary with the thickness of the film and the viewing angle.

Interference Conditions (Constructive and Destructive)

The conditions for constructive and destructive interference in thin films depend on the combination of the optical path difference and any phase shifts upon reflection. For destructive interference (resulting in minimal transmitted intensity), the conditions must be such that the two waves are out of phase. Conversely, constructive interference (leading to maximum transmitted intensity) occurs when the waves are in phase. These conditions guide the selection of wavelengths that are either suppressed or enhanced in the transmitted light.

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