A beam of light is incident from air on the surface of a liquid. If the angle of incidence is 25.5° and the angle of refraction is 15.6°, find the critical angle for the liquid when surrounded by air.

Фc = 38.66°

Explanation:

from Snell's law:

n1*sin (Ф1) = n2*sin (Ф2)

for air, n1 = 1.0

1.0*sin (Ф1) = n2*sin (Ф2)

n2 = 1.0*sin (Ф1) / sin (Ф2)

n2 = 1.0*sin (25.5) / sin (15.6) = 1.601

For the critical angle: Ф2 = 90° and n2 = 1.601

n2*sin (Фc) = n1*sin (Ф2) = n1

sin (Фc) = n1 / (n2*sin (Ф2))

sin (Фc) = (1.0) / (1.601*sin (90))

sin (Фc) = 0.625

Фc = 38.66°

Therefore, the critical angle is 38.66°