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学生在总复习机械波的时候,对由波形图线和其它条件来求传播速度和传播时间等这类问题往往感到很棘手。这里介绍一个对处理这类问题时很有用的结论。结论:如图1所示,实线为一列简谐波在某一时刻的波形图,虚线为△t秒后它的波形图。当波向右传播时,其传播速度为v正=(λn+△x′)/△t,(n=0,1,2……); 当波向左传播时,其传播速度为v反=[λ(n+1)-△x′]/△t,(n=0,1,2……)。结论证明:以虚线上M点为参考点。①波向右传播的情况:
When students review the mechanical wave in general, they often find it difficult to ask questions such as the speed of propagation and the time of flight from waveform charts and other conditions. Here is a useful conclusion for dealing with such issues. Conclusion: As shown in Fig. 1, the solid line is the waveform of a simple harmonic at a certain moment, and the dashed line is its waveform after Δt seconds. When the wave propagates to the right, its propagation velocity is v positive=(λn+Δx′)/Δt, (n=0,1,2...); When the wave propagates to the left, its propagation velocity is v= [λ(n+1)-Δx′]/Δt, (n=0, 1, 2, ...). The conclusion proves: Take M point on the dotted line as the reference point. 1 wave propagation to the right: