Snell's law formula as below
\[
n_{i} \sin \theta_{i}=n_{r} \sin \theta_{r}
\]
where
\[
\begin{aligned}
&n_{1}=\text { Refractive index of material } 1 \\
&n_{r}=\text { Refractive index of material } 2 \\
&\theta_{1}=\text { Angle of incidence } \\
&\theta_{r}=\text { Angle of refraction }
\end{aligned}
\]