Question

Why is the focal point for any convex lens a little inexact with ordinary white light?

• A. White light has a very long wavelength, compared to other colors.
• B. White light has a very short wavelength, compared to other colors.
• C. White light bends more than all the other colors.
• D. White light is made up of colors of light, which bend different amounts as they pass through the lens.
• E. White light bends less than all the other colors.

Answer 1

Answer: (D)

The focal length of a convex lens is given by

$\frac{1}{f}=(\frac{n_{material}}{n_{medium}}-1)\left(\frac{2}{R}\right)$

Since the refractive index of material is different for different colours, the focal length of the lens is different for them. Hence the constituents of white light bend by different amounts.