A beam of white light is incident normally on the surface AB of an equilateral prism ABC and emerges out of it suffering a deviation of `60^(@)`.
(a) Draw a diagram to show the path of beam till it emerges out of the prism. Mark the angles wherever necessary.
(b) What assumption have you made while drawing the diagram ?
(c) Name the phenomenon exhibited by the light beam.

Explanation

(a) The ray diagram is shown in Fig. 6.7. The beam of white light incident normally on the face AB of the prism passes undeviated inside the prism and strikes the other face AC at an angle of incidence of `60^(@)` At the face AC, it suffers total internal reflection. After total internal reflection at

the face AC, the beam of light falls normally on the face BC, so it emerges out without deviation.
(b) Assumption : The critical angle of glass-air interface is less than `60^(@)` for all colours of whitelight.
(c) Phenomenon : Total internal reflection.