Wave Propagation

Abstract

When a portion of a deformable medium is disturbed, it is deformed; the deformation disturbs the neighboring parts of the medium, and so propagates the disturbance through the medium. Such a disturbance is termed a wave and its progress through the medium is called wave propagation. As the wave propagates it carries energy in the form of kinetic and potential energies. The transmission of these energies is not by any bulk motion of the medium, but is passed on from one particle to the next. In other words, waves in deformable bodies are characterized by the transport of energy through motions of particles about an equilibrium position. Deformability and inertia of a medium are essential for the occurrence of waves. If the medium were not deformable, any part of the medium would immediately experience a disturbance upon application of a disturbance to a certain part of the medium, thus the response of the medium to the disturbance would be immediate, not gradual as in wave propagation. Similarly, if the medium had no inertia there would be no delay in the displacement of particles, and the transmission of the disturbance from one particle to another would be instantaneous. When a wave propagates through a three-dimensional medium, we can at a certain instant of time draw a surface through all points undergoing an identical disturbance. As time goes on, such a surface, which is called a wavefront, moves along. The normals to the wavefront, defining the direction of wave propagation, are called rays.