Suppose you are using total internal reflection to make an efficient corner reflector (see section 7). If there is air outside and the incident angle is 45.0º, what must be the minimum index of refraction of the material from which the reflector is made?

1.414

Explanation:

the critical angle is the minimum angle of incidence in the denser medium for which the angle of refraction in rarer medium is 90 degree.

the relation between the refractive index and critical angle is given by

n = 1 / Sin i

n = 1 / Sin 45

n = 1.414

thus, the refractive index of the material medium is 1.414.