Determine the limiting angle of incidence when the light beam passes from water to air.

In general, the law of refraction is written as:
sin a / sin b = n₂ / n₁ (1),
where a is the angle of incidence,
b – angle of refraction,
n₁ is the refractive index of the medium from which the ray falls on the interface,
n₂ is the refractive index of the medium into which the beam passes.
Air refractive index n₂ = 1 with high accuracy. For water, n₁ = 1.33.
If the angle b = 90 °, then sin b = 1.
Let’s rewrite (1) taking into account the last remarks:
sin a = 1 / 1.33;
a = arcsin (1 / 1.33) = arcsin (0.7518) = 48.75 °.
Answer: The limiting angle of incidence for water is 48.75 °.