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velocity of sound

# velocity of sound - Laboratory Report PHYS122L The Velocity...

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PHYS122L The Velocity of Sound in Air Purpose of the Experiment: To become familiar with the use of an oscilloscope to measure time-varying signals To measure the wavelengths of sounds in air using a direct measurement of phase shift To measure the wavelengths of sounds in air using Lissajous patterns To determine the phase velocity of sound in air To observe intensity drop-off with distance away from a sound source Experimental Procedure: A waveform generator is connected to a loudspeaker to produce sound of a particular frequency that can then be observed on an oscilloscope. Determining Phase Velocity of Sound: Method 1: Direct Measurement of a Phase Shift The waveform produced by the generator is compared to the waveform picked up by the microphone to determine the phase shift. The generator is set to produce a 1000 Hz signal. The microphone is placed about 5 cm from the loud speaker on a sliding track and is moved back until the peaks of the microphone signal are asymmetrically placed with respect to the peaks of the generator signal. The smaller of the two separations between the generator and microphone peaks is measured and used to compute a phase shift (negative), along with the position of the microphone on the track. The microphone is moved back in 5 cm increments as the phase shift and position are measured until the microphone has been moved back a total distance of 60 cm from the first data point. This procedure is repeated with a 3000 Hz signal. (For the first few measurements, the phase shift will be negative and decreasing in magnitude. After the microphone signal peak passes through the generator signal peak, the phase shifts should now be treated as positive.) The phase shift is calculated with the following equation: φ (x) = φ o + 2 π (x / λ ) where plotting phase versus x will have a slope of 2 π / λ . Method 2: Lissajous Figures The oscilloscope is changed to X-Y mode and the frequency is kept at 3000 Hz. Starting at the 15 cm position, the microphone is moved back until the Lissajous pattern corresponds to an “in phase” straight-line shape. The position of the microphone is recorded and it is slowly moved back until a “ π phase shift” straight-line shape is observed. This position is also recorded. This movement corresponds to one half of a wavelength. The microphone is continued to be moved back, recording the microphone’s position at each “in phase” and “ π phase shift” situation until it has moved through at least two full wavelengths. This procedure is then repeated using a 1000 Hz sine wave. Examining the Falloff of sound Intensity with Distance from a Loudspeaker:

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velocity of sound - Laboratory Report PHYS122L The Velocity...

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