Question

For a critical angle of ${60}^{\circ }$ and the refractive index of the first medium is 1.732, the refractive index of the second medium is:

• A. 1
• B. 1.5
• C. 2
• D. 2.5

Answer 1

The correct option is B 1.5

From the definition of Snell law, sin ${\theta }_c$ = $\frac{n_2}{n_1}$
To get $n_2$, put $n_1$ = 1.732 and ${\theta }_c$ = ${72}^{\circ }$
Thus we get, sin ${60}^{\circ }$ = $\frac{n_2}{1.732}$ and $n_2$ = 1.5