Question

The diagram shows the path of light through a right-angled prism of critical angle 42°. Observe the diagram and answer the questions that follow.

(i) Name the phenomenon at the surface of AС.

(ii) Determine the angle of incidence at the surface AC.

(ii) Determine the angle of incidence at the surface AB.

(iv) Which of the following statements is false?

1. The speed of light ray PQ is equal to the speed of light ray ST.
2. The speed of light ray QR is equal to the speed of light ray RS.
3. The speed of light ray PQ is greater than the speed of light ray RS.
4. The speed of light ray RQ is greater than the speed of light ray ST.

Answer 1

(i) Total Internal Reflection

(ii) In ΔCQR, ∠C = 60° and ∠Q = 90°.

Therefore, the angle with the surface ∠CRQ = 180° − (90° + 60°) = 30°.

Angle of Incidence = 90° − 30° = 60°

(iii) After reflection at AC, in ΔARS, ∠A = 30° and ∠ARS = 30°.

Therefore, the internal angle ∠ASR = 180° − (30° + 30°) = 120°.

Angle of Incidence = 120° − 90° = 30°

(iv) The speed of light ray RQ is greater than the speed of light ray ST.