A rectangular block of glass `ABCD` has a refractive index `1.6`. A pin is placed midway on the face`AB`, Fig. When observed from the face `AD`, the pin shall.
.

Options

A. appaer to be near `A`.
B. appear to be near `D`.
C. appear to be at the centre of `AD`.
D. not be seen at all.

Answer

A, D

Explanation

In Fig. apin is held at `L`, mid point of `AB`. When seen from face `AD` (so ling as `I lt C`) image of `L` appears to be at `L'`, closer to `A`.
From `sin C = (1)/(mu) = (1)/(1.6) = 0.625, C = sin^(-1)(0.625) = 38.7^(@)`.
So when angle of incidence becomes greater than `C (= 38.7^(@))`, the rays starting from `L` will undergo total internal refection and pin shall not be seen at all.
The choices (a) and (d) are correct.