Interference Question:(adsbygoogle = window.adsbygoogle || []).push({});

I'm trying to understand interference, I get the basic concept, that when two EM waves are superposed the resultant's amplitude of the vector sum of each original wave's respective amplitude. It's the following the creates confusion.

Picture the figure below. Wave A is a laser beam, and is traveling horizontally. Wave B is also a laser,m but has a propagation-path that intersects Wave A, such that at that point they are susceptible to interference (they are of the same frequency).

http://www.quia.com/files/quia/users/petetm/intersecting-lines.bmp

In the image, assume the waves are traveling in the directions their right-most arrows indicate (and that they travel in the same *general* direction), the actual angle is arbitrary, so long as it is small enough to ensure the waves superpose at the intersection-point.

Example 1: The waves, at the point of intersection, are 180 degrees out of phase, thus inducing destructive interference. If Wave A (horizontal) has an amplitude of 2, and Wave B an amplitude of 1, the resultant will have an amplitude of 1 (A= 2-1, A=1). But, does that mean that the output of wave A (the parts that propagate AFTER (to the right of) the point x (the point of intersection) will be a wave traveling along the path of Wave A and that has an amplitude of 1? Is it that the wave-train that has the larger amplitude (wave A in this case) will always be the one that retains a positive amplitude (in the case where destructive interference doesn't fully equal an amplitude of 0)? And likewise, if Wave B has an amp. of 2 and wave A had an amp of 1, would it be that propagation path of wave B that the resultant (with an amp of 1) travels along? Is this how interference works?

2nd question: Is there any way to make it so that both waves interfere destructively, but neither are fully negated, such that after that point of intersection both Wave A and Wave B have a lower amplitude? Perhaps thru not being fully out of phase, but out of phase by a fraction of a cycle? Or will this just reduce the magnitude of the decrease in the resultant's amplitude?

Details: I've heard that they interfere at that point, but then continue on their normal paths. But this doesn't seem to make sense; the resultant must travel in some direction, so wouldn't it be the one with the larger amplitude? Also, the first wave (which is negated in destructive interference) can't continue propagation, it was cancelled out, a wave with amp = 0 can't propagate.

I haven't been able to get a clear answer from other forums, so if someone could either verify or deny, and if deny explain exactly just what happens in these cases then, It would be very very much appreciated.

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# Interference Problem: Simple, but have't gotten a 'coherent' answer on other forums.

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