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Young's double slit experiment 
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#1
Feb2513, 09:42 PM

P: 83

Why did Young specifically perform a doubleslit experiment to demonstrate the wave nature of light, since light will diffract and interfere even through a single slit? Is there something special demonstrated by the doubleslit experiment that's not demonstrated by a singleslit experiment? (I'm specifically interested in the 19th century experiment...I understand the importance of the modern versions of the doubleslit experiment.)



#2
Feb2513, 09:52 PM

P: 8

in single slit experiment,light wil diffract but will not interfere as there is no path difference.
we will get a bigger circle of light than the slit on the shadow region. inorder to have interference there should be path bath difference,so we have two slits. wave nature could only explain interference. 


#3
Feb2513, 09:54 PM

P: 83




#4
Feb2513, 11:25 PM

P: 8

Young's double slit experiment
if we observe shadow region after diffraction, we have a bright circle and comparitvely darker circles around it,until it becomes dark...
we dont have maxima,minima and then again maxima. just make a small hole in a thick paper,pass light..you can observe 


#5
Feb2513, 11:34 PM

Mentor
P: 11,745

http://books.google.com/books?id=7AZ...page&q&f=false 


#6
Feb2613, 08:18 AM

P: 83

http://www.studyphysics.ca/newnotes/...t/lesson58.htm 


#7
Feb2713, 08:07 AM

P: 211

I believe your question on Young's original experiment has been answered.
Here is some information regarding your other question... Yes, there is a difference. Look at this wikipedia article under the section "Example: Difraction patterns" http://en.wikipedia.org/wiki/Envelope_(waves) There they say "The first factor, the singleslit result I1, modulates the more rapidly varying second factor that depends upon the number of slits and their spacing." 


#8
Feb2713, 08:13 AM

P: 211

"Noone has ever been able to define the difference between interference and diffraction satisfactorily. It is just a question of usage, and there is no specific, important physical difference between them." 


#9
Feb2713, 09:26 AM

Mentor
P: 11,745

http://hyperphysics.phyastr.gsu.edu...t/sinslit.html As for the difference between interference and diffraction, I think of interference as the more general phenomenon: the superposition of waves with different phases; whereas diffraction is one consequence of interference, namely the "bending" of light around obstacles. In setups with slits, we tend to associate the term "interference" with effects due to the superposition of waves from different slits, and "diffraction" with effects due to the superposition of waves from different points in the same slit. 


#10
Feb2713, 11:35 AM

Sci Advisor
Thanks
PF Gold
P: 12,132

The reason that the two slits experiment is used, these days and probably pretty soon after the Young's firest demo will almost certainly be because the results are so visually stunning and can't just be put down to the 'natural fuzziness' of light coming from a single one. The sinc function is just not very impressive, compared with a dozen or more obvious fringes of equal brightness.
imho, 'everything' in optics is diffraction  it's just that some images show the wave nature of light more than others. What we describe as interference is more of your Σ, whereas diffraction is more of your ∫. 


#11
Feb2713, 01:30 PM

PF Gold
P: 947

Sophiecentaur. Agree: it's more impressive.
The maths of predicting the pattern is also easier (if we neglect (treat as constant) the 'modulating factor' due to diffraction at each single slit). So we have a demonstration which is both impressive and simple to explain. [I think that Young, though much better educated than Faraday, was not especially interested in treating various cases of interference and diffraction mathematically. Fresnel was. In this respect Fresnel's work in wave theory might perhaps be compared to Young's as we compare Maxwell's work in electromagnetism to Faraday's.] 


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