Plasma media include stars, the solar and galactic wind, the upper atmospheres of various planetary bodies, flames, chemical and nuclear explosions, electrical discharges, and certain metals including copper, silver, and gold.Ī plasma medium may contain electromagnetic waves, as well as sound waves of various kinds. Normally, a plasma is a medium of gaseous matter which differs from other gas by its high temperatures, electrical and thermal conductivity, by complex particle and wave interactions, and by the emission of electromagnetic radiation. The various instabilities in a plasma medium generate spontaneous fluctuations which lead to the generation of sound.Ī plasma is a special state of matter which is characterized by the ionization of its particles. Plasma waves are produced by local disturbances caused by instabilities of the motions in a plasma medium. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License. We recommend using aĪuthors: Paul Peter Urone, Roger Hinrichs 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 Wavelength, frequency, amplitude, and speed of propagation are important for sound, as they are for all waves. (These processes can be viewed as a manifestation of the second law of thermodynamics presented in Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency.) Whether the heat transfer from compression to rarefaction is significant depends on how far apart they are-that is, it depends on wavelength. In addition, during each compression a little heat transfers to the air and during each rarefaction even less heat transfers from the air, so that the heat transfer reduces the organized disturbance into random thermal motions. But it is also absorbed by objects, such as the eardrum in Figure 17.6, and converted to thermal energy by the viscosity of air. The amplitude of a sound wave decreases with distance from its source, because the energy of the wave is spread over a larger and larger area. Pressures vary only slightly from atmospheric for ordinary sounds. The graph shows gauge pressure versus distance from the source. In solids, sound waves can be both transverse and longitudinal.) Figure 17.5 shows a graph of gauge pressure versus distance from the vibrating string.įigure 17.5 After many vibrations, there are a series of compressions and rarefactions moving out from the string as a sound wave. (Sound waves in air and most fluids are longitudinal, because fluids have almost no shear strength. These compressions (high pressure regions) and rarefactions (low pressure regions) move out as longitudinal pressure waves having the same frequency as the string-they are the disturbance that is a sound wave. But a small part of the string’s energy goes into compressing and expanding the surrounding air, creating slightly higher and lower local pressures. As the string oscillates back and forth, it transfers energy to the air, mostly as thermal energy created by turbulence. In this text, we shall explore such periodic sound waves.Ī vibrating string produces a sound wave as illustrated in Figure 17.3, Figure 17.4, and Figure 17.5. In many instances, sound is a periodic wave, and the atoms undergo simple harmonic motion. On the atomic scale, it is a disturbance of atoms that is far more ordered than their thermal motions. The physical phenomenon of sound is defined to be a disturbance of matter that is transmitted from its source outward. Ultrasound, for example, is not heard but can be employed to form medical images and is also used in treatment. But sound has important applications beyond hearing. Hearing is the perception of sound, just as vision is the perception of visible light. Because hearing is one of our most important senses, it is interesting to see how the physical properties of sound correspond to our perceptions of it. Sound can be used as a familiar illustration of waves. While the sound is not visible, the effects of the sound prove its existence. Figure 17.2 This glass has been shattered by a high-intensity sound wave of the same frequency as the resonant frequency of the glass.
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