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)=n_(2)`
B. total internal reflection occurs at AB for `n_(3) gt n_(1)`
C. the ray will return back to the same medium for alll values of `n_(3)`
D. total reflection occurs at CD for `n_(3) lt n_(1)`

Answer

C

Explanation

for combination of `n_(1)` and `n_(2)` crtical angle is `theta` when be places parallel slab of refractive index `n_(3)(n_(3) lt n_(1))`. Then crtical angle decreases and T.I.R. takes place for any value of `n_(3)` the ray will be return back in the medium `n_(2)` and reflection takes place at the surface CD.