Question

Draw an isosceles right angled prism and show how a ray of light can be turned through an angle of 90°. Assume prism is of glass and critical angle for glass is 42°.

Answer 1

1. The ray enters face AB normally and goes straight to the hypotenuse AC.
2. At AC, the angle of incidence (45°) is greater than the critical angle (42°), so the ray undergoes total internal reflection.
3. The reflected ray leaves face BC normally, so it is turned through 90°.