Question

A glass prism $ABC$ (refractive index 1.5), immersed in water (refractive index $\frac{4}{3}$ ). A ray of light is incident normally one face $AB.$ If it is totally reflected at the face $AC,$ then

• A. $sin\theta \geq \frac{8}{9}$
• B. $sin\theta \geq \frac{2}{3}$
• C. $sin\theta \geq \frac{\sqrt{3}}{2}$
• D. $\frac{2}{3} < sin\theta < \frac{8}{9}$

Answer 1

Answer: (A)

For total internal reflection at face $AC$
$sin\theta >\frac{\mu _{w}}{\mu _{g}}$
$\Rightarrow sin\theta \geq \frac{4}{3 \times 1.5}$
$\Rightarrow sin\theta \geq \frac{8}{9}$