Recall that the amount of diffraction of a wave is significant when the size of the opening is similar to the wave length of the wave and you can explain why sound waves diffract a great deal, while the waves of light do so to a much smaller extent. The emitted waves are semicircular, and occur at t, time later. Each point on the wavefront emits a wave at speed, v. where s is the distance, v is the propagation speed, and t is time. The principle can be shown with the equation below: s vt (26.2.1) (26.2.1) s v t. This is a result of refraction of sound waves caused by the cool air that lies above the water in the evening.įinally, have you ever considered why you are able to hear sounds coming through an open doorway even though you cannot see the source of that sound? This is caused by diffraction of the sound waves, which spread out into a broad angle when passing through the opening. SOUND WAVES, REFLECTION & REFRACTION Lecture No. Figure 1 shows a simple example of the Huygens’s Principle of diffraction. However, the waves spread out to some extent into the area beyond the gap. Reflection, Refraction, and Diffraction As mentioned briefly above, when light encounters an obstacle or an interface between two mediums, it can behave in one of several ways. If you have ever been at the shore of a quiet lake in the evening, you may have noticed how you can hear sounds coming across the lake that were not heard hours earlier during the daytime. When waves meet a gap in a barrier, they carry on through the gap. Sonar and ultrasound are two technologies that take advantage of the reflection of sound. Whether a sound wave is reflected, refracted, or absorbed depends on the densities of the materials either side of the boundary. Possible behaviors include reflection off the. Rather, a sound wave will undergo certain behaviors when it encounters the end of the medium or an obstacle. Refraction provides a reflection of the varying opaque nature of the two. The difference between refraction and diffraction is more of a description between the wave sources and their interaction with the elements to which it is exposed. The realities of diffraction may affect your choice of loudspeakers for your personal listening. Like any wave, a sound wave doesn't just stop when it reaches the end of the medium or when it encounters an obstacle in its path. Both light and sound waves undergo the effects of either type. The fact that we can hear an echo is an example of the ability of sound to reflect off surfaces. Note that the wavelength of the 100 Hz sound is about 3.45 meters, much larger than the speaker, while that of the 2000 Hz sound is about 18 cm, about the size of the speaker.
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