Answer:
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°
