Question

A light ray moving in medium- I (of refractive index $n_1$) is incident on interface of two media and it is totally internally reflected at the interface. Now refractive index $n_2$ of medium-II is decreased, then

• A. ray will be totally transmitted in medium-II.
• B. ray will move completely parallel to the interface,
• C. ray will be still totally internally reflected at interface.
• D. ray will be totally transmitted into medium-II only if angle of incidence is increased.

Answer 1

Answer: (C)

As $n_2$ decreases $, i_c = \sin^{-1} \left( \frac{n_2}{n_1} \right) $ also decreases, so condition $i > i_c $ is still satisfied and there will be still total internal reflection at interface. If angle of incidence is increased then ray will be still totally internally reflected at interface because $i > i_c$