Question

(a) A ray of monochromatic light enters glass PQRS as shown in the fig. Complete the path of ray till it emerges from the glass. (Critical angle of glass is 42⁰). 

(b) Draw diagram of a prism periscope.
(c) What are the advantages of total internal reflecting prism over plane mirror?

Answer 1

Note : here that when the angle of incidence in the denser medium is more than the critical angle (= 42), then the ray undergoes total internal reflection.

At angle of incidence equal to critical angle, the ray grazes the interface.

(b) Diagram of prism periscope:

(c)  In case of reflection from plane mirror, all of light in not reflected. In case of total reflecting prism, all rays failing beyond critical angle will be totally reflected. The intensity of reflected light is equal to the intensity of incident light in case of total internal ref;lection but not in case of reflection from plane mirror.

In addition, the reflection through a thick mirror causes multiple image formation as well as lateral inversion of image.

Due to the above two reasons, the total reflecting prisms are preferred over the plane mirrors.