Class 12 Physics Wave Optics | Reflection of plane waves |

**Reflection of plane waves **

- When all the points on an incident wave which are in same phase are considered together, incident wave front will be obtained.
- After reflection incident waves will bounce back.
- Waves which are lighter will touch the surface before the waves which are denser.
- Let the time taken by some portion of wavefront to interact with the boundary is τ.
- As soon as incident wavefront touches the boundary, every point on the incident wavefront will give rise to secondary wavelets.
- The wavefront for the secondary wavelets will be a sphere.
- After some time t
_{1}incident ray is at some other point, again it will give rise to wavefront. - Radius of the wavefront = velocity (speed) of the wave x time taken=vxτ.
- When other points interact with the boundary gradually, both τand radius will keep decreasing.
- As a result the tangent of all these points will give rise to reflected wavefront.
- Mathematically:-
- Speed of the wave =v
- Time taken by B to reach point C i.e. BC= vx τ
- At point A it will give rise to secondary waves, therefore radius=vτ.
- After some time τ will keep on decreasing.
- Therefore as it moves towards the point C the radius of the sphere (wavefront) will keep on decreasing.
- If a tangent is drawn then a reflected wavefront is obtained.

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