The source sound is a stick hitting a metal can. Sound Example : Multiple echoes produced under a parabolic bridge, Stanley Park, Vancouver, B.C. Sound Example : Reflected sound from the opposite side of a lake, heard as an echo. Compare: ABSORPTION, ACOUSTIC RADIATION, REFRACTION, TRANSMISSION. See also: BINAURAL HEARING, PHASING, SOUND PROPAGATION. Symmetrically-shaped surfaces produce symmetrical reflections, the most striking examples of which are the whispering gallery, where sound travels along the walls via repeated reflections, and the PARABOLIC REFLECTOR where all sound is reflected to the focus of the parabola. In general, concave surfaces focus sound waves, thereby concentrating the sound in specific areas, and convex shapes scatter sound, thereby promoting good diffusion. Different surfaces have different reflecting powers, as measured by their ABSORPTION COEFFICIENT or REFLECTION COEFFICIENT. Sound reflection gives rise to DIFFUSION, REVERBERATION and ECHO.
Reflection of a sound wave at a barrier, as if from an imaginary source at an equal distance behind the barrier. See: CANYON EFFECT, DIFFUSE SOUND FIELD, SOUNDING BOARD. 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. However, this law of reflection holds only when the WAVELENGTH of the sound is small compared to the dimensions of the reflecting surface. Waves can spread in a rather unusual way when they reach the edge of an object this is called diffraction. the angle of INCIDENCE of a SOUND WAVE equals the angle of reflection, just as if it were produced by a 'mirror image' of the stimulus on the opposite side of the surface. The law for reflection is the same as that for light, i.e. If a sound is not absorbed or transmitted when it strikes a surface, it will be reflected. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License. Use the information below to generate a citation. Then you must include on every digital page view the following attribution: If you are redistributing all or part of this book in a digital format,
Then you must include on every physical page the following attribution: If you are redistributing all or part of this book in a print format, Want to cite, share, or modify this book? This book uses the This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission. In addition, we will see that Huygens’s principle tells us how and where light rays interfere. It is useful not only in describing how light waves propagate but also in explaining the laws of reflection and refraction. Huygens’s principle works for all types of waves, including water waves, sound waves, and light waves. The new wave front is a plane tangent to the wavelets and is where we would expect the wave to be a time t later. We can draw these wavelets at a time t later, so that they have moved a distance s = v t. Each point on the wave front emits a semicircular wave that moves at the propagation speed v. A wave front is the long edge that moves, for example, with the crest or the trough. The new wave front is tangent to all of the wavelets.įigure 1.26 shows how Huygens’s principle is applied. Starting from some known position, Huygens’s principle states that every point on a wave front is a source of wavelets that spread out in the forward direction at the same speed as the wave itself. The Dutch scientist Christiaan Huygens (1629–1695) developed a useful technique for determining in detail how and where waves propagate. The direction of propagation is perpendicular to the wave fronts (or wave crests) and is represented by a ray. The view from above is perhaps more useful in developing concepts about wave optics.įigure 1.25 A transverse wave, such as an electromagnetic light wave, 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 wave fronts (or wave crests) as if we were looking down on ocean waves. A light wave can be imagined to propagate like this, although we do not actually see it wiggling through space. Huygens’s principle is an indispensable tool for this analysis.įigure 1.25 shows how a transverse wave looks as viewed from above and from the side. This is particularly true when the wavelength is not negligible compared to the dimensions of an optical device, such as a slit in the case of diffraction. However, some phenomena require analysis and explanations based on the wave characteristics of light. So far in this chapter, we have been discussing optical phenomena using the ray model of light. Use Huygens’s principle to explain diffraction.Use Huygens’s principle to explain the law of refraction.Use Huygens’s principle to explain the law of reflection.By the end of this section, you will be able to: