MCQ
A glass prism whose cross-section is an isosceles triangle stands with its (horizontal) base in water; the angles that its two equal sides make with the base are each $\theta$. An incident ray of light, above and parallel to the water surface is totally internally reflected at the glass-water interface and subsequently re-emerges into the air. Take the refractive indices of glass and water to be $\frac{3}{2}$ and $\frac{4}{3} $ , respectively. Maximum value of $cos\theta$ is.
- A$\sqrt {\frac{{20}}{{21}}}$
- ✓$\sqrt {\frac{{17}}{{21}}}$
- C$\sqrt {\frac{{7}}{{10}}}$
- D$\sqrt {\frac{{4}}{{9}}}$
