A monochromatic beam of light is incident at the interface of two materials of refractive index `n_1` and `n_2` as shown . If ` n_1 gt n_2` and ` theta_C` is the critical angle then which of the following statements is NOT true ?

Options

A. `theta_1 = theta_3` for all value of ` theta_1`
B. `cos theta_2 ` is imagimary for ` theta_1 gt theta_c`
C. ` cos theta_2 = 0` for ` theta_1 = theta_c`
D. ` cos theta_3 ` is imaginary for ` theta_1 = theta_c `

Answer

D

Explanation

` n_1 gt n_2`
this means light is going from rarer to denser medium so ` theta_2` will always be less than ` theta_1`
` n_2 sin theta_1 = n_1 sin theta_2`
so ` cos ( theta_2) ` will never be imaginary and also `theta_2` can .t be `90^@`
In question incorrect options are askd
` therefore (B,C,D)`