声速的测量 预习报告

声速的测量 预习报告 实验名称:声速的测量 实验目的:了解超声波的产生、发射和接收的方法，用干涉法(驻波法)和相位法测量声速。 实验原理: (一)为什么选择超声波进行测量。 在弹性介质中，频率从20Hz到20kHz的振动所激起的机械波称为声波，高于20kHz，称为超 48声波，超声波的频率范围在2×10Hz-5×10Hz之间。超声波的传播速度，就是声波的传播速度。超声波具有波长短，易于定向发射等优点，在超声波段进行声速测量比较方便。 本实验用压电陶瓷超声换能器来测定超声波在空气中的传播速度，它是非电量电测方法的一个例子。 实验装置 由波动理论可知，波速与波长、频率有如下关系:v = f λ，只要知道频率和波长就可以求出波速。本实验通过低频信号发生器控制换能器，信号发生器的输出频率就是声波频率。声波的波长用驻波法(共振干涉法)和行波法(相位比较法)测量。下图是超声波测声速实验装置图。 驻波法测波长 由声源发出的平面波经前方的平面反射后，入射波与发射波叠加，它们波动方程分别是: x,,, ,,yAcos2ft,,1,,, period of anti-Japanese war, Communist Party members such as Wang Huapeng, Chen Youqun operating from Zhejiang province came to the Tomb, widely publicized in the youth-Japanese thought. Shen Decai son Shen Bo (also known as Qing, Wei Qing), when only 13 years old, take part in activities at the outset, set up "Youth Club" book reading progress, once carried out revolutionary activities. Shen Decai does not drag, fully support the son, secretly help protect. Son watching progress not completed after the book, Shen Decai always putting books into hard wood mountain for safekeeping. In May 1941, the white terror is x,, ,,，yAcod2ft,,2,,, 叠加后合成波为: y = 2Acos2X/cos2ft,,,，，，， X =n/2 ,,当时称为波腹 y = 2Acos2X / =1,,, 当时，称为波节 X =2n+1/4 ,,cos2X/0,,,，，，， 因此只要测得相邻两波腹(或波节)的位置Xn、Xn-1即可得波长。 相位法测波长 从换能器S发出的超声波到达接收器S，所以在同一时刻S与S处的波有一相位差:, = 2,x/,1212 其中,是波长，x为S和S之间距离,。因为x改变一个波长时，相位差就改变2,。利用李萨如图12 形就可以测得超声波的波长。 实验记录 实验仪器及规格 YB1638 0.3KHz~3MHz函数信号发生器 游标 量程 30cm 精度0.02mm 实验温度前 22.5? 实验后温度22.8? 谐振频率 34.65KHz 实验一 驻波法测量声速 实验次数 1 2 3 4 5 6 7 8 9 游标读数/cm 9.408 9.910 10.420 10.932 11.442 11.948 12.450 12.960 13.472 实验次数 10 11 12 13 14 15 16 游标读数/cm 13.976 14.480 14.992 15.500 16.010 16.518 17.030 实验二 相位法测量声速 实验次1 2 3 4 5 6 7 8 9 10 数 游标读11.952 12.970 13.982 14.994 16.000 17.010 18.022 19.030 20.040 21.048 数/cm period of anti-Japanese war, Communist Party members such as Wang Huapeng, Chen Youqun operating from Zhejiang province came to the Tomb, widely publicized in the youth-Japanese thought. Shen Decai son Shen Bo (also known as Qing, Wei Qing), when only 13 years old, take part in activities at the outset, set up "Youth Club" book reading progress, once carried out revolutionary activities. Shen Decai does not drag, fully support the son, secretly help protect. Son watching progress not completed after the book, Shen Decai always putting books into hard wood mountain for safekeeping. In May 1941, the white terror is 数据处理 (一)计算实验室温度下声波理论速度 由实验记录 实验温度前 22.5? 实验后温度22.8? 22.522.8，,TC,,22.69知 实验平均温度 2 RT,0Vms,,331.45/由273K时空气中声速为 0M T22.6 VVms,，,，，,1331.451344.90/0T实验室温度下声速理论值 ，，273273 (二)驻波法测量声速的游标读数处理 实验要求 初始测量时,超生发生器与接收器之间要有至少5cm距离.在本次测量时,初始没有做到这一点.所以截取数据5~16来进行处理. 实验次5 6 7 8 9 10 11 12 13 14 数 游标读11.442 11.948 12.450 12.960 13.472 13.976 14.480 14.992 15.500 16.010 数/cm 实验次数 15 16 游标读数/cm 16.518 17.030 ,,,xxx波腹间的距离 ii，1 波腹 1 2 3 4 5 6 7 8 9 10 11 ,x/cm i period of anti-Japanese war, Communist Party members such as Wang Huapeng, Chen Youqun operating from Zhejiang province came to the Tomb, widely publicized in the youth-Japanese thought. Shen Decai son Shen Bo (also known as Qing, Wei Qing), when only 13 years old, take part in activities at the outset, set up "Youth Club" book reading progress, once carried out revolutionary activities. Shen Decai does not drag, fully support the son, secretly help protect. Son watching progress not completed after the book, Shen Decai always putting books into hard wood mountain for safekeeping. In May 1941, the white terror is