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# Coherence watch

1. I’m a bit confused about coherence.

I know two sources are coherent if they have a constant phase difference, does that mean in the image below, all the waves are coherent?

Even if the phase difference isn’t zero, are the waves still coherent as long as it’s constant?

https://imgur.com/a/1jf5z
2. Yes, as long as the phase difference isn't changing, the waves will remain coherent, provided they jave the same frequency.
Yes, as long as the phase difference isn't changing, the waves will remain coherent, provided they jave the same frequency.
So as long as the waves have the same frequency and same constant phase difference, they are coherent.
4. (Original post by JacobPowell)
So as long as the waves have the same frequency and same constant phase difference, they are coherent.
... actually does the phase difference need to be same, it just needs to be constant? @radioactiveDecay
5. Constant phase difference means every wave has and maintains its original phase angle throughout the course of their interactions

That's a condition for coherence
6. (Original post by Onlineslayer)
Constant phase difference means every wave has and maintains its original phase angle throughout the course of their interactions

That's a condition for coherence
So one wave could have a difference of 180 degrees, another 10 degrees and another 123 degrees, but as as long as it’s constant throughout, its coherent?
7. (Original post by JacobPowell)
So one wave could have a difference of 180 degrees, another 10 degrees and another 123 degrees, but as as long as it’s constant throughout, its coherent?
Yes exactly so.

In the mark scheme, if you dare say coherent waves must have equal phase angles, it's an automatic fail. one could even get arrested for that. hehehehe
8. (Original post by Onlineslayer)
Yes exactly so.

In the mark scheme, if you dare say coherent waves must have equal phase angles, it's an automatic fail. one could even get arrested for that. hehehehe

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