# Refraction and Prisms

1. Sep 6, 2015

### Alameen Damer

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?

2. Sep 6, 2015

### Staff: 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.

3. Sep 6, 2015

### Alameen Damer

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

4. Sep 7, 2015

### blue_leaf77

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

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Last edited: Sep 7, 2015
5. Sep 7, 2015

### sophiecentaur

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.....

6. Sep 7, 2015

### Staff: Mentor

That is the triangle I meant.
And the sum of those three angles is 180 degrees.