Question

A triangular prism of glass is inside water. A ray, inciden normally, on one of the faces, is totally reflected from face $BC$. Then the minimum refractive index of glass is -

• A. $\frac{\sqrt{3}}{2}$
• B. $\frac{5}{3}$
• C. $\frac{2\sqrt{2}}{5}$
• D. $\frac{4\sqrt{2}}{3}$

Answer 1

Answer: (D)

$\text{ For T.I.R. }45^{\circ }>C$
$\therefore \sin 45^{\circ }>\sin C$
$\therefore \frac{1}{\sqrt{2}}>\frac{4/3}{n}$
$\therefore n>\frac{4\sqrt{2}}{3}$