Experimental report Experimental topic: Measurement of sound velocity Experimental purpose: To understand the methods of generating, transmitting and receiving ultrasonic waves, and to measure sound velocity by interference method and phase method. Experimental content: 1 Measure the room temperature at the beginning of the experiment. 2 Standing wave method (1) puts two piezoelectric ceramic transducers of ultrasonic sound velocity instrument together. Check whether the two surfaces are level. If not, level them. (2) Connect the function signal generator to the transmitting end of the ultrasonic sound velocity measuring instrument, and connect the oscilloscope to the receiving end. The function signal generator selects sine wave, the output frequency is about 300HZ, and the voltage is10-20 V. (3) Observe the signal amplitude through the oscilloscope, adjust the distance between the two ends of the measuring instrument, find the position where the signal is particularly large, and use fine adjustment near the maximum value. That is, the screw that fixes the moving scale is adjusted with the fine-tuning nut. (4) From this extreme position, move the moving scale in one direction, and record the readings of the cursor in turn when the signal amplitude is extremely large (antinode). *** 12 value. Three-phase method (1) combines two piezoelectric ceramic transducers of ultrasonic sound velocity instrument. Check whether the two surfaces are level. If they are not horizontal, level them. (2) Connect the function signal generator to the transmitting end of the ultrasonic sound velocity meter, connect CH 1 of the oscilloscope to the receiving end, and connect CH2 to the transmitting end. Select CH 1 and X-Y superposition of CH2. The function signal generator selects sine wave, and the output frequency is about 300HZ. The voltage is 10-20V. (3) Observe Lissajous figure with an oscilloscope, adjust the distance between the two ends of the measuring instrument, and find the position where the figure is a straight line with positive slope. (4) From this position, move the ruler in one direction, and record the reading of the cursor in turn every time the graph is a straight line with positive slope, with the value of * * 10. 4 The measurement experiment is over. Take the average from the initial room temperature as the temperature t, arrange the instruments and arrange the experimental platform. 5. Calculate the difference L between the above two groups of data, then calculate the speed of sound V, and calculate the uncertainty. Calculate the relative error with the theoretical value of t calculation. The data processing 1 theoretical calculation shows that the temperature at the beginning of the experiment is 23.0℃, and the temperature at the end of the experiment is 2 1.8℃. Therefore, it is considered that the temperature during the experiment is t=22.4℃. According to the theoretical value, the vernier reading (mm) of 2 standing wave method is calculated. 95.42 100.50 105.70 1 10.66 1 15.88 120.90 126. 16 13 1.34 1 36.203610.1610.409.8810.5438+00.5388+00, when Because it is measured by an instrument similar to vernier caliper, the look-up table is Class B uncertainty, when P = 0.95, = 1.96. Therefore, the output frequency of acoustic wave is 34.3KHz, and the uncertainty is known. The speed of sound is right. There is an uncertainty transfer formula: the speed of sound in air v = (350.991.20) m/s (p = 0.95), and the relative error =3-phase vernier reading (mm). 110.80121.041.141.3615/. Therefore, the output frequency of sound wave is 34.3KHz, and the pair of sound velocities with uncertainty is known. There is an uncertainty transfer formula: the speed of sound in air v = (348.57 1 .09) m/s (p = 0.95) relative error = error analysis:1system error of the instrument itself and error caused by aging. The room temperature is constantly changing during the experiment. Whether standing wave method or phase method is used to find the maximum value on the oscilloscope. It is the subjective feeling of the measurer, and there is no accurate measurement. Question 1: Is it feasible to fix the distance between two transducers and change the frequency in order to obtain the sound speed? Answer: No. Because when the speed of sound is constant, the frequency changes and the wavelength changes, so it is impossible to measure the frequency and wavelength at the same time, and it is impossible to find the speed of sound. Wrong.