# Refraction and Prisms

That is a page from my textbook. The book mentions that the angle of incidence on the right side when added with the angle of the refraction equals 60 degrees. Why is that?

mfb
Mentor
Consider the triangle formed by the light ray in the prism and the two prism borders. The sum of the interior angles is 180°, and one angle is 60°. Everything else follows from geometry with the right angles there.

Which triangle? If you mean the one formed by the refracted ray, it is not a right angle triangle.

blue_leaf77
Homework Helper
Triangle ABC:
$$\angle A + \angle B + \angle C = 180^0$$
Or triangle formed by B, C, and the prism's apex.

#### Attachments

• Triangle.png
2.1 KB · Views: 423
Last edited:
sophiecentaur
Gold Member
2020 Award
Another way to look at it. The very top triangle has one angle of 60°. The other two angles are 90- i and 90-r etc. etc.....

mfb
Mentor
Another way to look at it. The very top triangle has one angle of 60°. The other two angles are 90- i and 90-r etc. etc.....
That is the triangle I meant.
And the sum of those three angles is 180 degrees.