1(vi)
The figure shows a source of light S at the bottom of a trough containing a transparent liquid. Rays X and Y emerge from the source. If ∠SOP = 43°, state the possible angle of incidence of ray Y.
- (a)43°
- (b)45°
- (c)47°
- (d)49°
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49°
Reason — Ray X grazes the liquid surface, so its incidence angle is the critical angle: 90° − 43° = 47°. Ray Y undergoes total internal reflection, requiring an incidence angle greater than 47°; hence, 49°.