Why Are Soap Bubbles Colored?
Little children love to watch and catch soap bubbles as they float in the air. Whether they are blown from a plastic pipe or just massed in a sink or bathtub, the bubbles seem to shimmer with colors that shift between blue, red and purple as they encounter even small amounts of light.
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Considerations
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The reason that soap bubbles are colored has to do with the physics of light. Light travels in straight lines from its source. While it looks white to our eyes, light is made up of a whole spectrum of colors. Each color is formed by a different wavelength of electromagnetic radiation. Our eyes can perceive only a small portion of the entire spectrum. We see light as violet, blue, green, yellow, orange and red.
Significance
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Light rays that hit a reflective surface, like a mirror, bounce back. When they encounter an opaque surface, they are blocked. If there is even a small hole in the opaque surface, light will diffract through the hole and spread out on the other side. When light rays move from one transparent medium to another, however, some rays go through, and some rays bounce back. The light rays that penetrate from one medium to another such as from air to water, for example, bend at the point where the air meets the water. When light bends it is called refraction.
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Function
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Refraction is what causes soap bubbles to be colored. The bubbles are a transparent medium through which light rays enter and bend. The more the light ray bends, the more blue from the spectrum will become visible to the human eye. Smaller bends make the red parts of the spectrum visible. In effect, the surface of the bubbles acts like a prism that separates the various light rays into their individual wavelengths, which look to us as colors.
History
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Two 17th-century Dutch scientists contributed the first descriptions of refraction. In 1621, Willebrond Snell explained the principles of how, when you look at a straight stick in a pond, it seems to bend. By 1678, Christian Huygens was able to build on this explanation to derive a formula for bending light.
Expert Insight
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This information became the key to optical prescriptions for glasses. Like bubbles, the lenses of glasses are curved, transparent surfaces that admit light. While glasses don't make everything look colored, they work because of the way light is refracted to adjust for whether the person needs an object to appear closer, farther or shifted in a specific direction.
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