✔ 最佳答案
The receiver can receive 2 waves from the transmitter, namely the one directed from the transmitter, the other one is reflected from the metal plate and transmit to the receiver.
There is a path difference between the two waves.
As the receiver moves from P to Q, the path difference between the two waves change correspondingly.
When the receiver moves to a position where path difference is the integral multiple of the wavelength, constructive interference occurs and hence a maximum in magnitude is resulted.
When the receiver moves to a position where path difference is the odd multiple of half the wavelength, destructive interference occurs and hence a minimum in magnitude is resulted.
There should be several maximum and minimum between P and Q, resulting in the graph B.
2009-04-13 19:57:31 補充：
You have mixed up reflection and refraction.
For reflection, of course some of the wave will be (transmitted) to the receiver by striking the metal plate.
