5. (15 points) A light ray falls at an angle $\alpha=60^{\circ}$ on the front surface of a parallel glass plate. The refractive index of the glass is $n=1.6$. By what angle is the ray, reflected from the back surface of the plate and exiting back through the front surface, deflected from the direction of the incident ray?
Answer: $60^{\circ}$

Solution. The described situation is illustrated in the figure.

![](https://cdn.mathpix.com/cropped/2024_05_06_8c28a90fad387a53d326g-4.jpg?height=380&width=616&top_left_y=1255&top_left_x=800)

We need to find the angle between rays 1 and 2. It is clear that the required angle is $180^{\circ}-2 \alpha=60^{\circ}$