CBSE Class 12 Physics Prism Deviation and Disprtion Solved Examples

CBSE Class 12 Physics Prism Deviation and Disprtion Solved Examples. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Ex.1 Light is incident on the side of a 30°– 60° – 90° prism , as shown in the figure. A thin layer of a liquid is spread over the hypotenuse of the prism. If the index of refraction of the prism is 1.5, find the maximum refractive index of the liquid in order that a ray passing normally through the 60°– base may be
totally reflected.
Sol. The angle of incidence of the hypotenuse is 60°. The ray is totally reflected if 60° ≥ θC where θC is the critical angle for the glass- liquid interface.

Ex.2 A ray of light fall normally on a refracting face of a prism of refractive index 1.5. Find the angle of the prism if the ray just fails to emerge from the prism.

Ex.3 The refractive indices of material of a prism for blue and red colours are 1.532 and 1.514 respectively. Calculate angular dispersion
produced by the prism if angle of prism is 8°.
Sol. Here,μ_b= 1.532 and μ_r = 1.514 A = 8° . Angular dispersion
= (μ_b – μ_r) A
= (1.532 – 1.514) x 8
= 0.018 x 8 = 0.144° .

Ex.4 Determine the angle of flint glass prism, which should be combined with a crown glass prism of 5° so as to give dispersion but no deviation. Given, for crown glass :

Ex.5 The dispersive powers of crown and flint glasses are 0.03 and 0.05 respectively. The refractive indices for yellow light for these glasses are 1.517 and 1.621 respectively . It is desired to form an achromatic combination of prisms of crown and flint glasses which can produce a deviation of 1° in the yellow ray. Find the refracting angles of the two prisms needed.
Sol. Suppose, the angle of the crown prism needed is A and that of the flint prism is A’. We have