Question

A glass prism is immersed in water as shown in the figure. When a beam of light incident is incident normally on the face $ab$ , it is internally reflected at the face $ad$ . If the refractive index of glass is $1.5$ and that of water is $4/3$ , then

• A. $sin\theta <(2/3)$
• B. $sin\theta >(8/9)$
• C. $(2/3)<sin\theta <(8/9)$
• D. None of these

Answer 1

Answer: (B)

$\theta >{\theta }_C$ , where ${\theta }_C$ represents the critical angle for the pair of media
$sin\theta >sin{\theta }_C$
$sin{\theta }_C=\frac{{\mu }_{rarer}}{{\mu }_{denser}}=\frac{4/3}{3/2}=\frac{8}{9}$
$sin\theta >\frac{8}{9}$