Define the term wavefront. Using Huygen's wave theory, verify the law of reflection.
A surface of constant phase is termed as a wavefront.
Let us consider a plane wave AB be incident on a reflecting surface and MN at an angle of incidence (i). Let be the time taken by the wavefront to advance from B to C. Let v be the speed of the wave. Then,
Now, to draw the reflected wavefront. Let's draw a sphere of the radius centred at A. Now, In accordance with Huygen's principle, the tangent plane to this sphere passing through point c will give the refracted wavefront.
Remember that,
Let us consider the triangles EAC and BAC,
So, by RHS,
Thus,
Hence, the angle of reflection and angle of incidence are equal, by Huygen's wave theory.