3 3  Reflection of a plane wave by a plane surface
We next consider a plane wave AB incident at an angle i on a reflecting
surface MN If v represents the speed of the wave in the medium and if t
represents the time taken by the wavefront to advance from the point B
to C then the distance
BC =  vt
In order to construct the reflected wavefront we draw a sphere of
radius vt from the point A as shown in Fig 10