Question

Copy the Fig. I and Fig. II. Both Figures show isosceles right angled glass prisms.

1. Trace the course of rays P and Q till the rays emerge out in (i) Fig. I, (ii) Fig. II.
2. Which ray gets only refracted in (i) Fig. I and (ii) Fig. II?
3. Which ray gets totally internally reflected in (i) Fig. I and (ii) Fig. II?
4. Which surface appears silvery in (i) Fig. I and (ii) Fig. II?

Answer 1

(a) Course of rays

1. Fig. I:
   • Ray Q falls normally on XZ and enters without bending.
   • Q strikes XY at 45°, is totally internally reflected, then strikes YZ at 45° and is totally reflected again.
   • Q then leaves XZ normally, turned through 180°.
   • Ray P is refracted towards the normal at XY, then refracted away from the normal at XZ, and emerges.
2. Fig. II:
   • Ray P falls normally on XY and enters without bending.
   • P strikes XZ at 45°, is totally internally reflected, and leaves YZ normally, turned through 90°.
   • Ray Q is refracted at XZ, then refracted again at XY, and emerges.

(b)

1. Fig. I: ray P
2. Fig. II: ray Q

(c)

1. Fig. I: ray Q
2. Fig. II: ray P

(d)

1. Fig. I: faces XY and YZ.
2. Fig. II: face XZ.

A surface where total internal reflection takes place looks silvery.