A monochromatic light wave is incident normally on a glass slab of thickness $d$, as shown in the figure. The refractive index of the slab increases linearly from $n_1$ to $n_2$ over the height $h$. Which of the following statement(s) is(are) true about the light wave emerging out of the slab?

• A

  It will deflect up by an angle ${\tan }^{-1}\left[\frac{\left({n_2}^2-{n_1}^2\right)d}{2h}\right]$
• B

  It will deflect up by an angle ${\tan }^{-1}\left[\frac{\left(n_2-n_1\right)d}{h}\right]$
• C

  It will not deflect
• Correct answer
  D

  The deflection angle depends only on $(n_2-n_1)$ and not on the individual values of $n_1$ and $n_2$

Hence, the correct answer is option: 'D'.