Optics: Fraunhofer diffraction - multiple slits | MIT Video Demonstrations in Lasers and Optics

[@sahilwaghmode7699]

thanks ... now i got practical idea of it

[@dakotamercer1679]

For the two slit interference pattern, I calculated the width of the principal maxima to be approx. 8.45 mm

[@arisoda]

maximum*? or are u talking about the distance between the first and second maxima?

[@dakotamercer1679]

@@arisoda For the first maxima to the left or right of the central maximum, I got 1.69cm. Now I believe, ideally, the separation between maxima are always equal, thus the distance between minima are equal. I took half of 1.69cm which is 8.45mm, as the distance between maxima are measured from their centers, thus half of 1.69 would be the width of one maxima. Let me know what you think, arisoda

[@arisoda]

@@dakotamercer1679 no I believe that is not correct, unfortunately. You are right that the separation between maxima and minima are always the same, but not for the center maximum. This one is always 2 times the width of a normal maxima/minima. That is because of diffraction. Correct me if I'm wrong. But 1.69 becomes actually the separation of 3 maxima.

[@csbootcamp7]

Quite Helpful !

[@arrabalimaz622]

wonderful

[@odal6770]

I get confused by "black lines", "spacings" and "slit width". Which us which? Are black lines opaque lines, and the spacings open? Or are spacings different from slits? Does not make much sense to me this way.

[@davidhaworth1802]

You might well ask! As far as I can determine, a Ronchi Ruling is a rather superior form of transmission diffraction grating, or at least that is how it is being used in this demonstration. The professor states that the black lines have thickness 75 microns and the separation between lines (which I assume to be centre of one black line to the centre of the next) is 125 microns. This makes the gaps between the black lines to be 50 microns wide. The separation between gaps is 125 microns being the centre of one gap to the centre of the adjacent gap. The professor is using the adjustable slit (with the razor blades) to illuminate a subset of the slits on the grating. You will note that he is also using a lens system to expand the laser beam to illuminate more of the grating, and thereby realise the resolution potential of the grating. What he doesn't say but has to be happening is that the expanded laser beam passing through the grating is in fact converging to a focus on the screen 200 cm away I hope this helps.

[@odal6770]

@@davidhaworth1802 R.I.P Ezekiel. He obviously did not agree with Feynman that this is the only mystery in physics. It is a nice example of the shut up and calculate philosophy. Also, he was not using his notes but rather commenting loosely on what he was doing. I am glad I did not have to do the homework. abut your comment on the lens focus. When I use a laser pen at more or less the same distance to the wall, and a slide with a single or double slit, I get a much smaller pattern, nowhere near the size of what is shown here.

[@davidhaworth1802]

@@odal6770 My comments related to the diffraction grating demonstration. The directions of constructive interference are according to a well-known formula. It is the same formula for the diffraction grating as for the double slit. Does the size of your pattern agree with your calculations?

[@odal6770]

@@davidhaworth1802 I don't doubt the formulas, it is a matter of geometry. I have my doubts on the presentation. Perspectives and size change with camera settings. It makes it very difficult to judge dimensions on the basis of a video clip.

[@odal6770]

@@davidhaworth1802 The screen markers are fixed, while the size of the pattern changes.

[@nightmisterio]

Did he say that is glass with slits?

[@rambabusl2757]

nice video

[@amirsohilkhan1910]

good

[@martinbe5111]

Looks like a 90's commercial