Diffraction and Interference

Why do soap bubbles and gasoline spills create different color reflections?

Iridescence is the spectrum of colors that are produced when light hits a thin film such as a soap bubble or gasoline layer. The interference of light waves resulting from reflections of light off the two surfaces of the thin film causes iridescence. A soap bubble displays an iridescent pattern because light reflects off the front and back surfaces of the soap bubbles. As the thickness of the layer varies, the interference between the two reflections will vary, causing the color to vary.

Gasoline spills are easily seen on wet roads; this is not because people spill more gas when it has rained, but is instead due to the iridescent patterns that result from light reflecting off of the top of the gasoline, and the boundary between the gasoline and water. The resulting pattern appears as the colors of the visible light spectrum in the thin film of gasoline.

Soap bubbles have an irridescent shine when light hits them because light waves reflect off the two surfaces of their thin film.

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