Question

A flashlight underwater (n=1.43) is aimed at the surface with incident angle 30°. What is the angle of refraction in the air (n=1) ?

Answer 1

The Snell's law says

$$n_i\sin\theta_i=n_r\sin\theta _r$$

Thus

$$\theta_r=\sin^{-1}\left(\frac{n_i}{n_r}\sin\theta_i\right)$$

$$\theta_r=\sin^{-1}\left(\frac{1.43}{1.00}\sin30^\circ\right)=45.6^\circ$$