Practice portal › Ray Optics and Optical Instruments › Refraction through a Prism
Asked in GUJCET 2016 · Dispersion and scattering
Idea: a lens is a piece of a dispersive material, and its focal length follows the refractive index through 1/f=(n-1)(1/(R₁)-1/(R₂)).
In any normal dispersive medium violet light has the larger index: n_V>n_R.
A larger n makes (n-1) larger, so 1/f is larger and f is smaller.
Therefore f_V<f_R, which is the same statement as f_R>f_V.
This colour-by-colour difference in focal length is chromatic aberration, the coloured fringe seen at the edge of an image formed by a single lens.
Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.
Practise this with a timer