01--- conditions for interference of two trains of waves at the meeting place

Problem description

There are two columns of light waves with the same frequency that meet and stack in space , If there is interference , The two waves do not need to have any conditions at the place where they meet ？
A. The direction of vibration is the same
B. The phase difference is constant
C. The amplitude difference is not too large
D. The propagation direction is the same

answer

The above questions should be D Options .

analysis

A Options ： First, light wave is divided into shear wave and longitudinal wave , Shear wave is a wave whose vibration direction is perpendicular to the propagation direction , Longitudinal wave is a wave with the same vibration direction and propagation direction . obviously , There is no interference between shear wave and longitudinal wave . therefore A Options exclude .
B Options ： If two waves want to produce interference fringes , There must be a constant phase difference . therefore B Options exclude .
C Options ： If the amplitude difference is too large , As you can imagine , The contribution of one train of waves to the final interference fringes can be neglected compared with the other train of waves , So it's not reasonable . therefore C Options exclude .
D Options ： The direction of propagation can be different , Such as standing wave , It is formed by the interference of two columns of light waves with exactly opposite propagation directions . So we should choose D.

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