In Figure, light is incident at an angle `theta` which is slightly greater than the critical angle. Now, keeping the incident angle fixed a parallel slab or refractive index `n_(3)` is placed on surface AB. Which of the following statements are correct?

Options

A. Total internal reflection occurs at AB for `n_(3) lt n_(1)`
B. Total internal reflection occurs at AB for `n_(3) gt n_(1)`
C. The ray will returen back to the same medium for all values of `n_(3)`
D. Total internal reflection occurs at CD for `n_(3) lt n_(1)`

Answer

a, c.

Explanation

(a) `rarr n_(3) lt n_(1)` so critical angle decreases. Therefore, TIR will take place at AB.
(b) `rarr n_(3) gt n_(1)`, so critical angle increases. Therefore, TIR will not take place.
(c) `rarr n_(3) gt n_(2)`, then TIR will take place CD and if `n_(3) gt n_(1)` , then TIR will take place at AB.
(d) `rarr` TIR will not take place at face CD for `n_(3) lt n_(1)` because ray is going from rarer to denser medium.