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Old Apr 20th 2017, 01:24 PM   #1
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I don't understand diffraction

So, I learned about diffraction in physics class, and I must say it's a bit of a mystery to me.

Here's the deal: I was told whether or not a wave diffracts through a gap in an obstacle depends on the size of the obstacle relative to the wavelength.

However, given a wave is technically a succession of signals: what if a single signal is sent towards that obstacle? If it's alone, it therefore doesn't have a wavelength, right? So does it diffract or not?

And if the answer is yes, why would it be different if we sent two of these signals, one after the other? Why would the two signals not simply both diffract one after the other?

If the wavelength between these signals is the right size, it would mean none of them would diffract, somehow? But that must mean these two signals interract with eachother? Which is just... Not the case.

So yeah, maybe I just haven't understood **** to waves, anyway please help.
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Old Apr 21st 2017, 05:41 AM   #2
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If you are talking about the "everyday" waves in water then obviously there is interaction (through the bulk of the water) between one wave and the next and between the wave and the water beyond the obstacle.

If you are talking about quantum objects then yes the situation is more difficult and people have been puzzling over it for decades.

Basically it has been found experimentally that photons, high speed electrons, etc. exhibit diffraction (and interference) behaviours just like "ordinary" waves.
But (as you indicate) this has strange implications when you try to consider individual electrons (etc.) as waves...
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