Question

The refractive index of glass is maximum for:
(A) Red colour
(B) Yellow colour
(C) Violet colour
(D) Green colour

Answer 1

Hint: For visible light \[\lambda \] is smallest for violet and greatest for red light.

Complete step by step solution: According to Cauchy equation
\[\mu = A + \dfrac{B}{{{\lambda ^2}}}\]
\[\mu \to \]refractive index
\[\lambda \to \]wavelength
For visible light \[\lambda \] is smallest for violet light and greatest for red light.

Hence \[\dfrac{B}{{\lambda _{red}^2}} < \dfrac{B}{{\lambda _{violet}^2}}\]
Thus, \[{\mu _{red}} < {\mu _{violet}}\]
i.e. µ is maximum for violet colour

Option (C) is correct.

Note: The refractive index of glass \[{n_g}\] is 1.52 and that of water \[{n_w}\] is 1.33. Since the refractive index of glass is higher than the water, the speed of light in water is faster than the speed of light through glass. The refractive index provides a measure of the relative speed of light in different mediums.