Wave Problem

1. Path difference at point Q = 1 x (1.5/6) m = 0.25 m

2. Since the first soft sound (destructive interference) occurs at mid-point between O and P, the soft sound at Q is the second order destructive interference. Thus,
0.25 = (2 - (1/2)) 入 where 入 is the wavelength
i.e. 0.25 = (1.5)入
入 = 0.167 m




2015-07-31 10:22:20 補充：
Some amendments to my calculation:
1.Path difference at point Q = 1 x [1.5/square-root(1.5^2+6^2)] m = 0.243 m
2. 0.243 = (2 - (1/2)) 入
入 = 0.162 m

2015-07-31 10:26:18 補充：
Q:因為OQ個distance=1.5 m,所以Q個path difference = (1.5)入,呢個推理係錯?
A: The equation: path difference = (1.5)入 is right. But the figure "1.5" in the equation is NOT the OQ distance of "1.5 m".

2015-07-31 10:29:13 補充：
(cont'd)...
The numeral "1.5" in the path difference equation is a pure number that gives the "order of destructive inteference", in contrast to the "1.5 m" of the length of OQ.