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October 16, 2019, 09:37:10 pm

Author Topic: 1998 Q6 - can someone help me?  (Read 619 times)  Share 

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715761

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1998 Q6 - can someone help me?
« on: October 31, 2010, 09:43:10 am »
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"When a beam of light passes through a very narrow single slit a pattern is produced on a screen. Explain what this pattern tells us about the nature of the individual photons that make up the beam of light."

*no idea*

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715761

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Re: 1998 Q6 - can someone help me?
« Reply #1 on: October 31, 2010, 10:20:40 am »
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OK I have another question: 2007 Q.5

blah blah blah....Neutron has a de Broglie wavelength of 2.0X10^-10
neutron beam is projected onto a metal crystal with interatomic spacing of 3.0X10^-10 m
Would you expect to observe a diffraction pattern?

I said no because the ratio was 2:3 so 0.667 which was less than one, but apparently, "significant diffraction will occur"

What? Whyyyyyy? O~O
Is that close enough or something?
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fady_22

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Re: 1998 Q6 - can someone help me?
« Reply #2 on: October 31, 2010, 10:43:43 am »
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It's "approximately equal to one", as the definition states.
Yep, it's close enough. :P
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cameron_15

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Re: 1998 Q6 - can someone help me?
« Reply #3 on: October 31, 2010, 10:45:51 am »
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For light and matter, to produce a diffraction pattern, the wavelength and the slit need to be of the same order magnitude. That is they are raised to the same power.

It's a little vague (and caught me out to!) but diffraction occurs at ratios of wavelength:slit as low as .01!

There's a bit on this in the A+ Notes book, but basically what Is in bold above is what you need to know.

« Last Edit: October 31, 2010, 10:47:53 am by cameron_15 »
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fady_22

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Re: 1998 Q6 - can someone help me?
« Reply #4 on: October 31, 2010, 10:53:17 am »
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It's a little vague (and caught me out to!) but diffraction occurs at ratios of wavelength:slit as low as .01!


Yes, but diffraction would be so minimal here that a diffraction pattern would really not be observed; the important thing here is that "significant diffraction" occurs when the ratio is approximately equal to or greater than one.
Also, diffraction is maximised when the ratio is 1.
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cameron_15

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Re: 1998 Q6 - can someone help me?
« Reply #5 on: October 31, 2010, 11:25:56 am »
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It's a little vague (and caught me out to!) but diffraction occurs at ratios of wavelength:slit as low as .01!


Yes, but diffraction would be so minimal here that a diffraction pattern would really not be observed; the important thing here is that "significant diffraction" occurs when the ratio is approximately equal to or greater than one.
Also, diffraction is maximised when the ratio is 1.

Yes definitely, but the question (as per this thread) is would a diffraction pattern be observed. Yes, it would be, it wouldn't be very significant though.
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715761

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Re: 1998 Q6 - can someone help me?
« Reply #6 on: November 03, 2010, 08:51:33 pm »
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Ah.... ok cool thanks c=

*shakes fist at misleading textbook*
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schnappy

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Re: 1998 Q6 - can someone help me?
« Reply #7 on: November 03, 2010, 10:36:00 pm »
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I'm interested in a response to the OP's inital question, as I do not see how a single slit produces an interference pattern. I would expect a bright fringe in the middle, that fades to darkness on either side.

Whatlol

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Re: 1998 Q6 - can someone help me?
« Reply #8 on: November 03, 2010, 10:37:05 pm »
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I'm interested in a response to the OP's inital question, as I do not see how a single slit produces an interference pattern. I would expect a bright fringe in the middle, that fades to darkness on either side.

well intresting thing is they shone one photon at a time through a slit.. and the interference pattern still occured
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schnappy

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Re: 1998 Q6 - can someone help me?
« Reply #9 on: November 06, 2010, 05:48:03 pm »
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Yes, but diffraction would be so minimal here that a diffraction pattern would really not be observed; the important thing here is that "significant diffraction" occurs when the ratio is approximately equal to or greater than one.
Also, diffraction is maximised when the ratio is 1.

This was my understanding, but a practice exam I did... turns out the 'greater than' but isn't true... atleast not in sounds' multiple choice. apparently the ratio must equal one. Could be the exam at fault, but something to be aware of.

shokstar

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Re: 1998 Q6 - can someone help me?
« Reply #10 on: November 07, 2010, 12:33:52 pm »
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The pattern represents the probability that a photon will strike. The bands are areas of high probability that a photon will strike there while the blank columns in between are the lowest probability that a photon will strike there, and it shows that photons have wave like properties, wave-particle duality blah blah blah. We were taught this in school and its also in the A+ notes book, its called 'Taylor's experiment'. Cant find a good website explaining it online, but that was with minimal googling.