Chapter 25, Problem 12Q

Explain why chromatic aberration occurs for thin lenses but not for mirrors.

To determine

Why chromatic aberration occurs for thin lenses and why not for mirrors.

Answer to Problem 12Q

Solution:

Chromatic aberration occurs in lenses due to dispersion when light passes through them. In case of mirror there is no dispersion as light is reflected from the smooth metallic surface. Hence, no chromatic aberration.

Explanation of Solution

In lenses chromatic aberrations occurs due to dispersion of light, that is different colors (or wavelengths)of light are bent by different amounts because of the varying refraction indexof most materials with wavelength. Thus, when a light passes through the lens, all colors of light donot come out at same angle result the different colors to focus on different positions.

In the case of mirror light gets reflected from the smooth metallic surface and all the colors of light are reflected at the exact same angle, thus there is no dispersion, and no chromatic aberrations.

In most mirrors, there is a piece of glass that covers the metallic reflector. The two faces of the glass is parallel and even refraction and dispersion happens inside this glass the emerging colors of light follows same direction and hence no dispersion is visible, thus no chromatic aberration.