Q 12-09-135JEE MainJEE Main 2022 (25 Jun, Shift 1)Medium
A light wave travelling linearly in a medium of dielectric constant $4$ is incident on the horizontal interface separating the medium from air. The angle of incidence for which the total intensity of the incident wave will be reflected back into the same medium will be: (Given: relative permeability of medium $\mu_r = 1$)
Answer: (D) $60^\circ$
Refractive index $n = \sqrt{\mu_r\varepsilon_r} = \sqrt4 = 2$. Critical angle: $\sin C = \dfrac1n = \dfrac12\Rightarrow C = 30^\circ$.
Total internal reflection needs $i > C$; among the options only $60^\circ$ works.
Solution by Sreeraj P, M.Sc Physics