Question

calculate the angle of incidence of light ray incident on surface of a plastic slab of refractive index
$\sqrt{3}$
,if the angle of refraction is 30 degree

Answer 1

sin i/sin30 =root 3
sin i =root 3×1/2
i=60 degree

Answer 2

Given that,

Refractive index of a plastic slab is $\sqrt{3}$

The angle of refraction is 30 degrees

To find,

The angle of the incidence of light ray.

Solution,

The ratio of sine of angle of incidence to the sine of angle of refraction is equal to refractive index of the medium. So,

$n=\dfrac{\sin i}{\sin r}$

i is angle of incidence

$\sin i=n\times \sin r\\\\\sin i=\sqrt 3\times \sin (30)\\\\i=\sin^{-1}\left(0.866\right)\\\\i=59.99^{\circ} \approx 60^{\circ}$

So, the angle of incidence is 60 degrees.