![]() ![]() size 12 about three times smaller than the width of the doorway. Each point on the wavefront emits a semicircular wave that moves at the propagation speed v. A wavefront is the long edge that moves, for example, the crest or the trough. In this part of Lesson 3, we will investigate behaviors that have. ![]() Possible behaviors include reflection off the obstacle, diffraction around the obstacle, and transmission (accompanied by refraction) into the obstacle or new medium. The new wavefront is a line tangent to all of the wavelets.įigure 10.5 shows how Huygens’s principle is applied. Rather, a sound wave will undergo certain behaviors when it encounters the end of the medium or an obstacle. Starting from some known position, Huygens’s principle states that every point on a wavefront is a source of wavelets that spread out in the forward direction at the same speed as the wave itself. Sound bounces off the surface of the medium which can be a solid or a liquid. The Dutch scientist Christiaan Huygens (1629–1695) developed a useful technique for determining in detail how and where waves propagate. An example of diffraction phenomena is given by the spreading of waves around an obstacle. Just like the reflection of light, the reflection of sound is similar as it follows the laws of reflections, where the angle of reflection is equal to the angle of incidence and the reflected sound, the incident sound, and the normal sound belong in the same plane. The direction of propagation is perpendicular to the wavefronts, or wave crests, and is represented by an arrow like a ray. ![]() The view from above is perhaps the most useful in developing concepts about wave optics.įigure 10.4 A transverse wave, such as an electromagnetic wave like light, as viewed from above and from the side. The side view would be a graph of the electric or magnetic field. From above, we view the wavefronts, or wave crests, as we would by looking down on the ocean waves. These pits have the same width and are equally spaced in a row, forming a diffraction grating on the CD mirror surface. Recorded data on CD is stored in tiny pits of different lengths, which carry the information. A light wave can be imagined to propagate like this, although we do not actually see it wiggling through space. Another example of diffraction is while observing the back of a compact disc (CD). 6.4, 7.2)įigure 10.4 shows how a transverse wave looks as viewed from above and from the side. 6.C.4.1 The student is able to predict and explain, using representations and models, the ability or inability of waves to transfer energy around corners and behind obstacles in terms of the diffraction property of waves in situations involving various kinds of wave phenomena, including sound and light.The information presented in this section supports the following AP® learning objectives and science practices: Discuss the propagation of transverse waves.Diffraction determines the direction in which most sound will be radiated, an important factor for the acoustical engineers who work to make them as quiet as possible.By the end of this section, you will be able to do the following: The white region is a cross-section of the front part of an aircraft engine, the sound wave is produced by the turbofan. The animation below shows another example of diffraction. Thus, this solution for noise reduction is efficient only if the houses are located within the shadow region of the sound barrier. It is characterised by low noise levels due only to the acoustic diffracted wave. A shadow region is observed just behind the barrier (bottom right of the animation). Interference patterns due to the superposition of the incident wave and the diffracted wave are clearly seen just before the barrier (bottom left of the animation). The animation below illustrates how a travelling wave emitted from the upper left corner by, say, an aeroplane is diffracted by a sound barrier erected to shield homes from the traffic noise. This bending of a wave is called diffraction. Another common example of diffraction is the contrast in sound from a close lightning strike and a distant one. For example, if a stereo is playing in a room with the door open, the sound produced by the stereo will bend around the walls surrounding the opening. An example of diffraction phenomena is given by the spreading of waves around an obstacle. The fact that diffraction is more pronounced with longer wavelengths implies that you can hear low frequencies around obstacles better than high frequencies, as illustrated by the example of a marching band on the street. Diffraction occurs if a wave encounters an object and if the wavelength is of the same size (or greater than) the object size. The spreading of waves when they pass through an opening, or around an obstacle into regions where we would not expect them, is called diffraction.
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