Question

Why does light refracting from water to air not follow Snell's law?

Answer 1

It does follow Snell's Law (`n_1sintheta_1=n_2sintheta_2`) for small angles of incidence `theta_1`.
However, as the angle of incidence becomes bigger, so does the angle of refraction `theta_2` until eventually the angle of refraction is `90^@`.
At this stage, the angle of incidence is called the critical angle `theta_c` for that interface for light passing from an optically more dense to less dense medium. (`n_1>n_2`)
As soon as the angle of incidence exceeds the critical angle, (`theta_1>theta_c`) then total internal reflection occurs and obeys the Law of Reflection. (`theta_1=theta_2`).