Practice portal › Ray Optics and Optical Instruments › Refraction through a Prism
Asked in CBSE AIPMT 2000 · Dispersion and scattering
Idea: follow one sunbeam through a single raindrop.
It refracts as it enters, and because μ depends on colour the colours fan out — that is dispersion.
The fanned beam reaches the back of the drop beyond the critical angle and is reflected back inside.
It refracts once more on leaving, and the colours reach the eye along slightly different directions, forming the arc.
So a rainbow is formed by dispersion together with total internal reflection.
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