Chapter 22 - Reflection and Refraction of Light - Learning Path Questions and Exercises - Exercises - Page 775: 35

$43^{\circ}$

For coin to be illuminated, light beam after refraction on the water should hit the coin in the water. Now, $tan\theta_{r}=\frac{0.9}{1.5}=\frac{3}{5}$ Which gives us $\theta_{r}=31^{\circ}$ By Snell's law, $n_{a}sin\theta=n_{w}sin\theta_{r}$ Thus, $1\times sin\theta= 1.33\times sin31^{\circ}$ Hence, $\theta = 43^{\circ}$