Objective: Determine the velocity of ultrasonic waves in liquids
The periodic variations of density caused by an ultrasonic standing wave pattern in a liquid act as an optical grating for the diffraction of a monochromatic parallel light beam that is transmitted in the direction perpendicular to the direction of the ultrasound wave. From the diffraction pattern and the known wavelength of the light, it is possible to determine the sound wavelength and use that to calculate the velocity of sound in the liquid.