Question

What is the meaning of wavefront? Explain the laws of reflection by explaining Huygens' principle of wavefront.

Hint:

Huygens’ principle is useful in explaining wave phenomena like reflection, refraction, and diffraction geometrically.

Answer 1

Definition of Wavefront:
A wavefront is defined as the continuous locus of all the particles of a medium that are vibrating in the same phase.
It is a surface over which the phase of the wave is constant.
Depending on the source of disturbance, wavefronts may be:

Spherical wavefronts – from a point source.

Cylindrical wavefronts – from a linear source.

Plane wavefronts – when the source is very far away.
Huygens' Principle:
According to Huygens’ Principle:

Every point on a given wavefront acts as a fresh source of secondary wavelets.

The secondary wavelets travel in all directions with the same speed as the original wave.

The new wavefront is the forward envelope of all these secondary wavelets.

Laws of Reflection Using Huygens' Principle:
Let a plane wavefront strike a reflecting surface. According to Huygens:

Each point on the incident wavefront acts as a source of secondary wavelets.

The reflected wavefront is formed by drawing tangents to all secondary wavelets.

By geometry, we find that: \[ \angle \text{incidence} = \angle \text{reflection} \] Thus, Huygens’ construction proves the laws of reflection.