Problem 5.16

Two optical media have a plane boundary between them. Suppose $\theta_{1 c r}$ is the critical angle of incidence of a beam and $\theta_{1}$ is the angle of incidence at which the refracted beam is perpendicular to the reflected one (the beam is assumed to come from an optically denser medium). Find the relative refractive index of these media if $\sin \theta_{1 c r} / \sin \theta_{1}=\eta=1.28$