1:51 I LTE ED Q 1 of 5 + > > LAB 5 Sound Waves 1. Purpose To study physical characteristics of sound waves. 2. Introduction We focus our attention now on sound waves, which travel through any material, but are most commonly experienced as the mechanical waves traveling through air that result in the human perception of hearing. As sound waves travel through air, elements of air are disturbed from their equilibrium positions. Accompanying these movements are changes in density and pressure of the air along the direction of wave motion. Download the Phyphox app onto your cell phone. Start Phyphox and select the Audio Amplitude tab which records short intervals from the microphone and calculates the sound pressure level (SPL). The sound pressure level (SPL) is the pressure level of a sound, measured in decibels (dB). It is equal to SPL(dB) = 20 log10 (p) = 10 log10 (Po) Eq. 1 where P is the absolute sound pressure, Po is the reference of sound pressure equal to 2 X 10" Pa, The sound intensity level is given by SIL(dB) = 10 10g10 To I is the absolute intensity, and I. = 10-12 W/m is the reference sound intensity. In this lab your cell phone/phyphox app will provide recording SPL values as a function of time. You will be exporting this data from your phone to your computer. Then with Matlab you will be able to calculate the mean values and the standard deviation of the SPL values. Using this mean value, you can then rearrange Eq. 1 to obtain the pressure amplitude P given by Spl P = Po X 10 20 Eq. 2 In terms of P the expression for the intensity is given by PHYS 1006E-Lab 5 Instructions Page 1 of 5 p2 2pv Eq. 3 where p is the density of air and v is the speed of sound in air. Table 1 gives these values for air as a function of temperature. Table 1: Effect of temperature on properties of air. Speed of Density Temperature, sound, c of air, p T (C) m/s) (kg/m3) 35 351.88 1.1455 30 349.02 1.1644 25 346.13 1.1839 20 343.21 1.2041 15 340.27 1.2250 10 337.31 1.2466 5 334.32 1.2690 331.30 1.2922 Download 8 Print a d21.laurentian.ca1:52 I LTE ED Q 2 of 5 + > > 1 = pz 2 pv Eq. 3 where p is the density of air and v is the speed of sound in air. Table 1 gives these values for air as a function of temperature. Table 1: Effect of temperature on properties of air. Speed of Density Temperature, sound, c of air, p T(C) (m/s) (kg/m) 35 351.88 1.1455 30 349.02 1.1644 25 346.13 1.1839 20 343.21 1.2041 15 340.27 1.2250 10 337.31 1.2466 5 334.32 1.2690 0 331.30 1.2922 -5 328.25 1.3163 -10 325.18 1.3413 -15 322.07 1.3673 -20 318.94 1.3943 -25 315.77 1.4224 Ref: WikipediaR Assuming an isotropic source, the intensity at a distance / from the sound source is given by 1 = = Power _ Power Eq. 4 where the Power is the average power emitted by the source expressed in Watts. The intensity decreases as the square of the distance from the source, an inverse square law. PHYS 1006E-Lab 5 Instructions Page 2 of 5 Question 1 A fireworks rocket explodes at a height of 100 m above the ground. An observer on the ground directly under the explosion experiences an average sound intensity of 7.00 x 10-2 W/m' for 0.2 s. (a) What is the total amount of energy transferred away from the explosion by sound? (b) What is the SIL level (in decibels) heard by the observer? 3. Materials Give a list of materials used to conduct the experiment. Include when applicable the uncertainties. 4. Procedure Include a photo and schematic diagram of your experimental set-up. Properly label the figures Calibration: Place the phone at about 4ft from a sound source. Specify the sound source you are using. For calibration it needs to be a sound source mimicking normal conversation speech. Proceed to phyphox app and select Audio Amplitude. Go to calibration. Now enter 60 db for the reference SPL and push calibrate while the experiment is running. After 30 seconds, stop the acquisition. Record the calibration offset. Measurement 1: Place your phone somewhere within the range 30-70 cm from the sound source. State your distance Li + Oz, . Measure the SPL as a function of time for 20 seconds from the sound course If noseible conduct Download Print a d21.laurentian.ca