Explain the reflection of a plane wave using Huygen's principle.

Explanation

Consider a plane wave AB incident at an angle i on a reflecting surface MN.
The velocity of wave in medium is v and `tau` is time to move the wavefront from point B to C.
`:.BC=vtau`

As shown in figure plane wave AB is incident on reflective surface MN and its reflective wavefront is СE.
In figure `DeltaEAC and DeltaBAC` are similar triangles, Here, `AE=BC=vtau`
`angleAEC=angleABC`
and AC=AC
hence `angleBAC=angleECA`
`:.i=r` is the law of reflection.