Question

Diagram alongside, shows a ray PQ incident normally on the equilateral prism ABC. Copy the diagram.

1. Complete the ray diagram, showing the emergence of ray in air.
2. What is the angles of incidence on (i) face AB, (ii) face АС.

Answer 1

(a)

1. Ray PQ falls normally on face AB, so it enters the glass without bending.
2. It meets face AC at R at an angle of incidence of 60°. This is more than the critical angle (42°), so the ray is totally internally reflected.
3. The reflected ray RS falls normally on face BC, so it leaves the prism into air along ST without bending.

(b)

• (i) Face AB: angle of incidence = 0°
• (ii) Face AC: angle of incidence = 60°