Question

When light travels from an optically denser medium to a rarer medium, why does the critical angle of incidence depend on the colour of light?

Answer 1

The critical angle for a given pair of medium is given by

`Sin "i"_"c" = (1)/mu`

where μ is the refractive index of the denser medium. The refractive index of a medium depends on the wavelength by the relation

`mu = "A" + "B"/lambda^2`

and each colour of light is associated with a specific wavelength, so as the wavelength of light increases critical angle increases.