Question

Why there is no backward wavefront?

Answer 1

Wavefront:

1. A wavefront is a surface upon which the phase of disturbance is the same at any given instant of time.
2. It is the loci of points of constant phase.
3. A wave travels in a direction normal to the wavefront.
4. Wavefront is the locus of all the particles in the same state of vibration.
5. The flow of energy does not happen from the lower potential to the higher potential.
6. Therefore, there is no backward wavefront, flowing from lower disturbance to higher disturbance.
7. In the case of a point source in an isotropic medium, the wavefronts are spherical surfaces.
8. Such waves are called spherical waves.
9. For linear sources wavefronts are cylindrical and corresponding waves are called cylindrical waves.
10. When the loci of points of constant phase lie on parallel planes the wavefronts are called planes and the associated waves are called plane waves.
11. At a sufficient distance from a source, a small portion of the wavefront may be taken as a plane.
12. In many optical devices, we produce light resembling plane waves.