Undergraduate experiment to measure the speed of sound in liquid by diffraction of light

摘要

Diffraction of light by an ultrasonic phase grating enables a direct measurement of the wavelength of acoustic waves in liquids. If the acoustic frequency is known independently, it can be combined with the measured acoustic wavelength to determine the speed of sound in liquid. The method of Debye and Sears based on a visual display of the diffraction pattern on a distant screen is used. Measurements carried out with a He-Ne laser and an ultrasonic nebulizer provide an excellent experiment for an undergraduate laboratory with a minimum of equipment. A sound velocity of 1536 m/s with an uncertainty of 1% is obtained for distilled water. (C) 2002 American Association of Physics Teachers. [References: 7]