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Draconis
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How do you measure path difference off a diagram? (Edexcel PHY4, June 2003, if anyone has the paper).
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CJN
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You can do s2-s1 if you have a diagram, which is the longer - the shorter lines that represent light.

Otherwise you can do it:

For maxima just do "N x Theta", where N is the maxima number (eg. 1, 2, 3) and theta is the wavelength. For minima it is "(N + 1/2) x Theta".
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Draconis
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(Original post by CJN)
You can do s2-s1 if you have a diagram, which is the longer - the shorter lines that represent light.
That's the thing that's confusing me. I have a source of microwaves, going through two slits. A maximum at point O and one at point X. I'm supposed to measure the path difference between O and X. How?
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Moronic Acid
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(Original post by Draconis)
That's the thing that's confusing me. I have a source of microwaves, going through two slits. A maximum at point O and one at point X. I'm supposed to measure the path difference between O and X. How?
I haven't got the paper in front of me, but if you count how many maxima X is away from O, and then multiply this by \lambda (wavelength) this should give the path difference
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Draconis
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(Original post by Moronic Acid)
I haven't got the paper in front of me, but if you count how many maxima X is away from O, and then multiply this by \lambda (wavelength) this should give the path difference
No maxima between X and O.. I don't have the wavelength.
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Moronic Acid
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I found the Edexcel June 03 paper but i can't see this question
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Draconis
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(Original post by Moronic Acid)
I found the Edexcel June 03 paper but i can't see this question
Oops, January 2002.

http://www.ktaggart.com/physics/Work...sQuestions.doc
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Draconis
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I'm trying to determine the wavelength. Mark scheme says path difference x 3, but I don't get where they get the path difference from..
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0le
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Surely you use that double slit formula?

http://www.matter.org.uk/schools/Con...e/formula.html
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Moronic Acid
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(Original post by Draconis)
I'm trying to determine the wavelength. Mark scheme says path difference x 3, but I don't get where they get the path difference from..
Yeah that is a bit weird - especially since they've asked you to use measurements from the diagram

I would've thought \lambda = \frac{xs}{D} should be used for this question
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0le
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Phase difference is used when you have nodes (minimum displacement) and anti-nodes (max displacement).
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Draconis
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(Original post by Moronic Acid)
Yeah that is a bit weird - especially since they've asked you to use measurements from the diagram

I would've thought \lambda = \frac{xs}{D} should be used for this question
On the mark scheme it says use of that formula is incorrect.
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0le
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Strange. Maybe its to do with harmonic frequencies? At the point 0 maximum, there is constructive superposition and the path difference is zero.
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Moronic Acid
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(Original post by Draconis)
On the mark scheme it says use of that formula is incorrect.
I literally have no idea why the term 'path difference' has been used
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Draconis
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CJN
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(Original post by Draconis)
That's the thing that's confusing me. I have a source of microwaves, going through two slits. A maximum at point O and one at point X. I'm supposed to measure the path difference between O and X. How?
Ok thats young's slits (thats what we used for light anyway) because that way one source can be used to generate both sets of waves.

Can you scan/draw in paint a picture of the problem you need to solve?

Assuming I understand you right then you can see my paint drawn picture

You can see the distances between the slit (P) and the two maxima, O and X.

The distances between P & O and P & Q are S1 and S2. The longer is S2 and shorter is S1.

So if P->O is 1m and P-> Q is 2m then its s2-s1 so 2-1 = 1m so the path difference is 1m.

Also what level is this at?
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