![]() The points on the limited wavefront going through the hole are so close together that their radiations take the form of a hemisphere. 11-2B except that the aperture is very small and only a small amount of energy passes through it. In a later paper Sommerfeld (1901) extended his analysis to the diffraction of pulses and treated the case of a ‘ rectangular pulse’ in detail. 11-2A, each wavefront passing through the aperture becomes a row of point sources radiating diffracted sound into the shadow zone. The diffraction of a simple harmonic wave train by a straight-edged semi-infinite screen, and by an infinite wedge, was originally discussed by Sommerfeld (1895). ![]() The sound energy at any point in the shadow zone can mathematically be obtained by summing the contributions of all of these point sources on the wavefronts. Have a look at this a simulation of three. Diffraction can be clearly demonstrated using water waves in a ripple tank. The amount of diffraction (spreading or bending of the wave) depends on the wavelength and the size of the object. c f, c f, where c 3.00 × 108 c 3.00 × 10 8 m/s is the speed of light in vacuum, f is the frequency of the electromagnetic wave in Hz (or s 1 ), and. As we have seen previously, light obeys the equation. Huygens' principle can be paraphrased as:Įvery point on the wavefronts of sound that has passed through an aperture or passed a diffracting edge is considered a point source radiating energy back into the shadow zone. Waves can spread in a rather unusual way when they reach the edge of an object this is called diffraction. We know that visible light is the type of electromagnetic wave to which our eyes responds. The same principle also gives a simple explanation of how sound energy is diverted from the main beam into the shadow zone. (B) If the aperature is small compared to the wavelength of the sound, the small wavefronts which do penetrate the hole act almost as point sources, radiating a hemispherical field of sound into the shadow zone.įor an answer, the work of Huygens is consulted.1 He enunciated a principle that is the basis of very difficult mathematical analyses of diffraction. Such problems can occur in auditorium with balconies. However, because of edge diffraction some sound will creep into this but such penetration is frequency dependent - high frequencies are less diffracted than low frequencies. These wavefronts act as lines of new sources radiating sound energy into the shadow zone. Sound shadow - Any barrier interrupting a sound wave will create a shadow (light). (A) An aperature large in terms of wavelength of sound allows wavefronts to go through with little disturbance. By what mechanism is this diversion accomplished? The arrows indicate that some of the energy in the main beam is diverted into the shadow zone. ![]() The wavefronts of sound strike the heavy obstacle: some of it is reflected, some goes right on through the wide aperture. Figure 11-2A illustrates the diffraction of sound by an aperture that is many wavelengths wide. ![]()
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