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 t1 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.

.