Huygen's Principle Definition: Every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.
Huygen’s Reflection: The tangent to these wavelets shows that the new wavefront has been reflected at an angle equal to the incident angle.
This is known as the law of reflection
​i.e., angle of incidence = angle of reflection
The direction of propagation is perpendicular to the wavefront, as shown by the downward-pointing arrows.
Explanation:
From the above equation, we can see that according to Huygen's principle for reflection of the plain waves the law of reflection can be expressed as