Explain the wavefront and its types.

(N/A) When we drop a small stone into a calm pool of water,waves spread out from the point of impact. Every point on the surface starts oscillating with time; hence,at any instant,the surface shows circular rings where the disturbance is maximum.
All points on such a circle are oscillating in phase because they are at the same distance from the source. Such a locus of points,which oscillate in phase,is called a wavefront. Thus,a wavefront is defined as a surface of constant phase.
The speed with which the wavefront moves outwards from the source is called the speed of the wave.
The energy of the wave travels in a direction perpendicular to the wavefront.
$A$ line perpendicular to the wavefront,indicating the direction of propagation of the wave,is called a ray. Hence,the wavefront and the ray are perpendicular.
Types of wavefronts:
$1$. Spherical Wavefront: If a point source emits waves uniformly in all directions,the locus of points having the same amplitude and vibrating in the same phase are spheres (in three dimensions). This is known as a spherical wavefront,as shown in figure $(a)$. Such waves are diverging.
$2$. Plane Wavefront: At a large distance from the source,a small portion of the sphere can be considered as a plane. It is known as a plane wavefront,as shown in figure $(b)$.
$3$. Cylindrical Wavefront: Wavefronts originating from a linear source and propagating in a three-dimensional homogeneous and isotropic medium are cylindrical wavefronts. For example,waves emanating from a tubelight,as shown in figure $(c)$.