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利用超声波遇到物体发生反射,可测定物体运动的有关参量.如图 (甲)中仪器A和B通过电缆线连接,B为超声波发射与接收一体化装置,仪器A为B提供超声波信号源而且能将B接收到的超声波信号进行处理并在屏幕上显示其波形.现固定装置B,并将它对准匀速行驶的小车C,使其每隔固定时间T0发射一短脉冲如图(乙)中幅度大的波形,而B接收到的由小车C反射回的超声波经仪器A处理后显示如图(乙)中幅度较小的波形.反射滞后的时间已在图(乙)中标出.其中T0、T和△T为已知量,另外还知道该测定条件下声波在空气中的速度为v0

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