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# Quick question on Intereference

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1. Hi

am I correct in saying that a wave undergoes constructuve intereference when it is pi/2 in phase and undergoes destructive interference when it is pi out of phase?
2. (Original post by DonWorryJockIsHere)
Hi

am I correct in saying that a wave undergoes constructuve intereference when it is pi/2 in phase and undergoes destructive interference when it is pi out of phase?
No I think it's 2Pi in phase => constructive (because it's the same wave on top of each other)
And then Pi out of phase => destructive
3. A circle is made of 2pi radians. I usually imagine that the mean-peak/ peak -down to mean etc is like a quarter of a circle, and 4 of those comprises a circle, so a wave takes 2pi to complete a full oscillation. Basically every time it goes from min to max is 180 degrees or half a circle (pi radians)

So when the peaks are the same, it's constructive. And this happens a full oscillation apart, so it's 2pi... A full circle. If it was pi radians out, then a peak would be with a trough, and it would be destructive.

So multiples of 2pi, or 360 degrees, will be constructive.
If it is pi out, then it is totally destructive
Numbers in between will produce a really noisy interference - At times it will be constructive, then destructive, then somewhere in between.

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