Measurement of Sound Speed in Liquid Using Optical Approach

Abstract:

An optical method to determine a speed of sound (or ultrasound) in water was described in this work. The measuring system composes of ultrasonic transducer, glass water bath, He-Ne laser source, lens, and screen. An ultrasound fog generator used for producing an ultrasound with a frequency f of 1.74 MHz was immersed in DI water. It was fixed at one side of water bath. When the sound wave travels in water along the length of water bath, a standing wave is obtained from the interference of the incidence wave and the wave reflected from the opposite side of water bath. The node and antinode of the standing wave act as an opaque and transparent medium. As a He-Ne laser beam with a wavelength of 632.8 nm travelled to a convex lens with a focal length of 5 cm and diverged through the sound field, an enlarged standing wave pattern was shown on a white screen. The wavelength of sound wave λ was obtained using geometry (similar triangle). Therefore, the speed of ultrasound in water was calculated by v = fλ. In this work, the water temperature was varied in a range of 15 - 39 °C. The results showed that the speed of sound increased with increasing the water temperature. The percentage error was below 2.8. This proposed method can be used for demonstrating physics principles such as waves and optics for high school students and undergraduates.

• Periodical: Advanced Materials Research (Volume 979)
• Pages: 75-78
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.979.75
• Online since: June 2014
• Authors: Pattanan Meethom, Kheamrutai Thamaphat*, Pichet Limsuwan, Orrawan Rewthong
• Keywords: Physics Education, Speed of Sound, Standing Wave, Ultrasound

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