question_answer

A ray of light is incident normally on an isosceles right angled prism of glass of refractive index 1-5 as shown in the figure. Which of the following figures correctly depicts the path of the ray as it passes through the prism?

A)                                                              

B)

C)                                                         

D)

Correct Answer: A

Solution :

 The incident ray is incident normally on face\[AC\], so angle of refraction at face \[AC\] is also zero. Angle of incident i, which the ray makes with normal to face \[AB\] is\[{{45}^{o}}\]. Since this angle is greater than critical\[(={{\sin }^{-1}}\frac{1}{1\cdot 5}=41\cdot {{8}^{o}})\], the ray suffers total internal reflection. Now\[,\]\[i=r\]. The reflected ray from the face \[AB\] is now incident on face\[BC\], at angle of incidence again \[{{45}^{o}}\] and for the same reason it is turned back as shown in the above figure.