B17: New Technologies & Resources for Teaching Undergraduate Physics

Wed. April 3, 10:45 a.m. – 10:57 a.m. PDT

Ballroom B4, Floor 2

Measuring the speed of sound in air is among the experiments conducted in introductory physics laboratory courses. Purpose of this re-visit is to improve accuracy with the use of current technologies in data collection. In the classic resonance-tube method, a tuning fork of known frequency and adjustable water level with a reservoir can (or other means) are used and the resonance condition is obtained by hearing the sound when it is loud. Instead, a speaker driven by a function generator and a sound sensor can be employed for more accurate results, where the resonance condition is obtained by means of the FFT display of the sound sensor. Here, eyes are used in addition to the ears to locate the resonance condition accurately. A magnifying glass is used to measure the meniscus of the water level. In addition, the sound sensor can be used in the echo method, where a PVC pipe (length = 1.52 m and diameter = 2.5 cm) closed on one end is used, and the time for echo is measured using the data collection software. In this method, a sound pulse is created by snapping the fingers close to the sound sensor, which is held at the open end of the pipe. Resulting multiple echoes of the pulses and their phase changes due to reflection are used in finding the travel time for an echo accurately. Accepted value is obtained using temperature, gas constant and ratio of specific heats and average molar mass for air, which is comparable within 1-2% of the measured values of the speed of sound in air using the resonance and echo methods.