Hair/wire laser diffraction interference pattern

AI Thread Summary
The discussion centers on the interference pattern observed when a laser shines on a hair or wire, questioning whether it resembles single-slit or double-slit interference. Participants note that the observed pattern appears more like single-slit interference, as the next bright fringe is dim, despite theoretical considerations suggesting a double-slit model due to light bending around the hair's edges. Babinet's Principle is referenced to explain the diffraction and interference effects, emphasizing that the pattern results from a single light source. The meaning of 'y' in the context of the hair-laser experiment is also explored, indicating its significance in measuring fringe distances. Overall, the experiment illustrates complex diffraction phenomena, reinforcing the need for visual aids to fully grasp the underlying principles.
esdoublelef
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Hair/wire laser diffraction interference pattern - does it follow single-slit or double-slit?

for single-slit interference, the equation nλ = d (y/D), (d is the width of the single-slit, y is the distance between central BRIGHT fringe to the nth DARK fringe, D is the distance from slit to screen)

for double-slit interference, the equation nλ = d(y/D), (d is the width of the single-slit, y is the distance between central BRIGHT fringe to the nth BRIGHT fringe, D is the distance from slit to screen)

How about for a laser shining on a hair (to find the thickness of hair/wire?), what does nλ = d (y/D) mean for the interference pattern?

Experimentally, the actual interference pattern I observe in class is that it looks like a single-slit (the next bright fringe isn't very bright, quite dim) . But when I draw a diagram to show how light bends around the edges of the hair, it looks like double-slit.

More importantly, what does y mean for the hair-laser experiment?

thanks!
 
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The pattern of light forming on the other side of the hair is a result of diffraction and interference and of cause some of the undistrubed beam getting past the hair. Is this pattern formed by a single source of light?
 
andrevdh said:
The pattern of light forming on the other side of the hair is a result of diffraction and interference and of cause some of the undistrubed beam getting past the hair. Is this pattern formed by a single source of light?

Yup it's a single source of light, and i suppose it'll be the same as single slit experiment. It's just trying to understand why, but i got to draw out the lines to understand it. Thanks all!
 
esdoublelef said:
Yup it's a single source of light, and i suppose it'll be the same as single slit experiment. It's just trying to understand why, but i got to draw out the lines to understand it. Thanks all!
I don't think it's easy to understand Babinet's principle by drawing rays or wavefronts. Instead, the elementary explanations that I've seen generally use an indirect argument. The link I posted gives a brief explanation. More of this type of argument can be found by web search and also here on the forum:
https://www.physicsforums.com/threads/why-does-laser-on-a-hair-wire-creat-a-single-slit.465358/
 
The wire presents the wavefronts coming from the laser with two edges, one on the left and one on the right.
 

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