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Asked in CBSE AIPMT 1994 · Dispersion and scattering
Idea: 1/f is proportional to (μ-1), and by Cauchy's relation μ falls as the wavelength rises.
The longest visible wavelength therefore has the smallest refractive index and the smallest power.
The smallest power means the longest focal length.
Of blue, green, yellow and red, red has the longest wavelength.
So the focal length of a convex lens is maximum for red light.
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