4. When a light ray passes from a material of higher n to a material of lower n

Question

4. When a light ray passes from a material of higher n to a material of lower n (for instance, a light ray passing from glass to air), the refracted angle is larger than the incident angle. In this case, the angle of the incident ray can exceed a critical angle, at which the angle of the refracted ray is 90 degree. For incident angles greater than the critical angle, there is no refracted ray, only a reflected ray. This phenomenon is called total internal reflection. What is the critical angle for water with n = 1.33? What is the critical angle for glass n = 1.50?

Explanation / Answer

by snell's law

sin(i) / sin(r) = n2 / n1

in case of critical angle, angle of recraction will be 90 degree

for water

sin(i_c) / sin(90) = 1 / 1.33

critical angle i_c = 48.75 degree

for glass

sin(i_c) / sin(90) = 1 / 1.50

critical angle i_c = 41.81 degree

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