A light ray passes from air into glass of refractive index $n = 1.5$ at an angle of incidence $\alpha = 30°$. Find the angle of refraction $\beta$.
The law of refraction (Snell's law):
$$\frac{\sin \alpha}{\sin \beta} = n \Rightarrow \sin \beta = \frac{\sin \alpha}{n}$$
$$\sin \beta = \frac{\sin 30°}{1.5} = \frac{0.5}{1.5} = \frac{1}{3} \approx 0.333$$
$$\beta = \arcsin 0.333 \approx 19.5°$$
$\beta \approx 19.5°$