**CBSE NOTES CLASS 12 PHYSICS **

**CHAPTER 10 WAVE OPTICS**

**Reflection of a plane wave by a plane surface**

Consider a plane wave front AB incident at an angle i on a reflecting surface MN. If v represents the speed of the wave in the medium, τ represents the time taken by the wave front to advance from the point B to C then the distance BC = vτ

Let CE represent the new wave front. Now AE = BC = vτ

Triangles EAC and BAC are congruent and therefore, the angles **i** and **r** would be equal. This is the **law of reflection**.