Wavefront and Types of Wavefronts :
Define wavefront. Discuss various types of wavefronts namely spherical wavefronts, cylindrical wavefronts and plane wavefronts.
Definition of Wavefront :
Wavefront is defined as the locus of all the particles of a medium vibrating in the same phase at a given instant. The shape of a wavefront depends upon the shape of the source of disturbance.
Types of Wavefronts :
(a) Spherical wavefront (SWF):
If the source of disturbance is a point source (O), then the wavefront is spherical. A point source of light emits waves which spread outward in all directions. If the medium is homogeneous, then after time $t$ seconds, the wave or disturbance will travel a distance equal to $vt$(sphere radius), from the point source in all directions.
In means, the particles of the medium lying on the surface of the sphere of radius $vt$ will get disturbed at the same moment i.e., all these particles will vibrate in the same phase. In this case, the spherical surface passing through these particles (equidistant from O and vibrating in the same phase) is called spherical wavefront.
(b) Cylindrical wavefront (CWF):
If the source of disturbance is a slit AB (i.e., line source), then the wavefront is cylindrical because all the points equidistant from line source lie on the surface of a cylinder.
(c) Plane wavefront (PWF):
At a very large distance from the point source, a small part of the spherical wavefront appears plane and this part of the spherical wavefront is called plane wavefront. Thus, a cylindrical wavefront appears as plane wavefront after travelling a large distance from the line source.
