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# Path Difference and Interference - Quincke's Tube Watch

1. Hi there.

I'm struggling with the question above - I calculated the wavelength of the light which is

340/800 = 0.425m

I'm not too sure where to go from there

Any help will be appreciated - Thanks
2. Bump - Any ideas?
3. (Original post by CrazyFool229)
Bump - Any ideas?
well have you thought about the condition for destructive interference?

also note that for every 1mm you alter D2, the path length in the RHS pipe goes up by 2mm.

PS you mean sound, not light don't you?
4. (Original post by Joinedup)
well have you thought about the condition for destructive interference?

also note that for every 1mm you alter D2, the path length in the RHS pipe goes up by 2mm.

PS you mean sound, not light don't you?
Yeah, sorry I did mean sound.

I did think that for destructive interference to occur it must be 1/2 wavelength path difference minimum which will be 0.2125m of the wavelength - Idk where to from there.
5. Also this might sound stupid - But how did you get the ratio for D1 and D2?
6. Can anyone help?
7. (Original post by CrazyFool229)
Also this might sound stupid - But how did you get the ratio for D1 and D2?
well the vertical length of both pipes is the same and fixed - but the RHS pipe can be lengthened in the horizontal direction - the sound waves have to left to right by D2 and then right to left by D2 - so horizontally it's a 2 way trip.

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