physics wave

Interference occurs at P. That is because the wave from the dipper directly to P and the reflected wave from the barrier interfere with each other.

The wave from the dipper is being reflected in the barrier, in the horizontal distance which is mid-point of the dipper and P.

For constructive interference, path difference = m入

For destructive interference, path difference = (m + 1/2)入

where m is a non-negative integer

Wavelength, 入 = 2 cm

For A, the path difference = 2 X sqrt[(10/2)2 + 52] - 10 = 10(sqrt2 - 1) = 5(sqrt2 - 1)入, which is not the above two situations.

For B, the path difference = 2 X sqrt[(16/2)2 + 52] - 16 = (sqrt89 - 8)入, which is not the above two situations.

For D, the path difference = 2 X sqrt[(32/2)2 + 52] - 32 (sqrt281 - 16)入, which is not the above two situations.

For C, the path difference = 2 X sqrt[(24/2)2 + 52] - 24 = 2 = 入, so the two waves interfere constructively.





2009-06-07 17:46:15 補充：
The wave is being reflected at the mid-point, it is because the incident angle = reflecting angle.