Question

Which of the following quantities related to a lens does not depend on the wavelength of the incident light?

• A. Refractive index
• B. Focal length
• C. Power
• D. Radii of curvature

Answer 1

The correct option is A Refractive index

For spherical mirror the focal length remains unaffected with all the three parameters wavelength, frequency and oscillation. The focal length of lens varies directly with the wavelength of light used and as wavelength is inversely related to refractive index, the focal length also varies inversely with it. This is the principal cause of chromatic aberration. The frequency of the light has no effect on the focal length. So, the focal length increases with wavelength but decreases with refractive index and vice versa.