Snell's law and total internal reflection in code

You will write three functions about light at a boundary.

The idea. Snell's law is $n_1\sin\theta_1 = n_2\sin\theta_2$. When $\sin\theta_2$ would be larger than $1$, there is no refracted ray: the light is totally reflected. The critical angle exists only when light goes from a denser to a rarer material, and then $\sin C = \dfrac{n_2}{n_1}$. For a view straight down, the apparent depth is the real depth divided by $n$. Angles are in degrees.

Your tasks.

1. In refraction_angle, return $\theta_2$ in degrees. Return None when the light is totally reflected.
2. In critical_angle, return $C$ in degrees. Return None when $n_1$ is not larger than $n_2$.
3. In apparent_depth, return the apparent depth for a view straight down.