Chapter 23. The law of reflection (23-1)

Review

The line \(BB'\) in Figure 23-4a is perpendicular to the incident wave front and so points in the direction of the incident ray. Likewise, the line \(AA'\) is perpendicular to the reflected wave front and so points in the direction of the reflected ray. We can determine how these directions are related to each other by noticing that the triangles \(ABB'\) and \(AA'B'\) are both right triangles, both have the same hypotenuse of length \(AB'\), and both have one side of length \(v_1\Delta{t}\) (Figure 23-4b). You can see that these two right triangles are identical, except that triangle \(AA'B' \)has been flipped left-to-right compared to triangle ABB9. So the angle \(\theta_1'\) of the line \(AA'\) measured from the vertical (that is, from the normal to the boundary) must be the same as the angle \(\theta_1\) of the line \(BB'\) measured from the vertical. We conclude that