A rainbow is an atmospheric optical arc produced by refraction, internal reflection and wave dispersion of light in water droplets. Wavelength-dependent refractive index separates the colours. The primary arc involves one internal reflection, and the secondary arc involves two.
For the one-internal-reflection branch, Snell's law and give . At an interior stationary point, , hence . Another differentiation gives there. The interior minimum exists for . The internal specular reflection can be partial; total internal reflection is not required.
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"Rainbow" can refer to several different concepts, depending on the context. Here are a few of the most common meanings: 1. **Natural Phenomenon**: A rainbow is a meteorological phenomenon that occurs when sunlight refracts, reflects, and disperses through water droplets in the atmosphere, resulting in a spectrum of light appearing in the sky.