Question

(i) Plot a graph to show variation of the angle of deviation as a function of angle of incidence for light passing through a prism. Derive an expression for refractive index of the prism in terms of angle of minimum deviation and angle of prism. 

(ii) What is dispersion of light ? What is its cause ? 

(iii) A ray of light incident normally on one face of a right isosceles prism is totally reflected as shown in fig. What must be the minimum value of refractive index of glass ? Give relevant calculations.

Answer 1

(i)

(ii) The phenomenon of splitting of white light into its constituent colours.

Cause : Refractive index of the material is different for different colours According to the equation, δ  A, where A is the angle of prism, different colours will deviate through different amount.

(iii)