回顾现象:多普勒效应——由于波源和观察者之间有相对运动,使观察者感觉(接收)到的频率与波源发出的频率发生变化的现象.两个关键物理量,一是波源发出的频率用f表示,二是观察者接收到的频率用f′表示.1当波源和观察者相对介质都静止如图1所示,图中一条斜线代表一个波长,在t_0到t的时 Retrospective Phenomena: Doppler Effect - A phenomenon that causes the observed (received) frequency of the observer to change with the frequency of the wave source due to the relative motion between the wave source and the observer. Two key physical quantities, one from the wave source The frequency is represented by f, and the frequency received by the observer is denoted by f ’.1 When the wave source and observer are stationary relative to the medium, as shown in Figure 1, a diagonal line represents a wavelength, t_0 to t