y(x,1)=y(x,1)+y2(x, △P∝sn(k-Ot)=[2 ym cos(△小/2)]sm(kx-0ot-) → The phase difference: 2 △=A-k=k-n=2△,△L=-1 △△L (1922) 2I 2 When AL=mn( m=0, 1, 2 (1923) The intensity reaches a maximum value, forming constructive interference When AL=(m+x)a destructive interference occurs The intensity has a minimum value   L =  2 , 2 | | | |  = k r1 − k r2 = k r1 − r2 = L    (19-22) sin( ) 1 P  k r −t The phase difference: 1 2 L = r − r When ( m=0,1,2,…...) (19-23), The intensity reaches a maximum value, forming constructive interference. When destructive interference occurs. The intensity has a minimum value. L = m ) 2 1 L = (m + [2 cos( / 2)]sin( ) ( , ) ( , ) ( , ) ' 1 2 =  − − = + y k x t y x t y x t y x t m