Light enters a substance from air at 30 degrees to thenormal.

It continues through the substance at 23 degrees tothe normal. What

would be the critical angle for thissubstance?

The angle of incidence and refraction are both measured from the normal

angle of incidence = 30°

angle of refraction = 23°

refractive index (n) = sini / sinr

n = sin30°/sin23°

n = 1.27965

refractive index (n) = 1/sinC

where C is the critical angle.

sinC = 1/n

C = arcsin (1/n)

C = arcsin (1/1.27965)

C = 51.39°