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Author Topic: Suposition of several waves  (Read 15661 times)
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Fu-Kwun Hwang
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on: January 28, 2011, 09:40:59 am » posted from:Taipei,T'ai-pei,Taiwan

The following simulate suposition of several sinwaves (n=1-5).

user can adjust wavelength, period, slit width and number of sources.

Enjoy!

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Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
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* wave_singleslit.jpg (53.4 KB, 510x511 - viewed 510 times.)
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ahmedelshfie
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Reply #1 on: January 28, 2011, 04:24:18 pm » posted from:SAO PAULO,SAO PAULO,BRAZIL

WOW, i like too much  the design of applet.
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lookang
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Reply #2 on: January 31, 2011, 08:56:21 am » posted from:Singapore,,Singapore

hi prof!

can make your ejs applet to allow to show this?


reference:
http://ngsir.netfirms.com/englishhtm/Diffraction.htm
A wave spreads out (noticeable diffraction) when the size of the slit is comparable to or smaller than the wavelength.

When waves reach a narrow slit, the water in the slit vibrates like a point source. The waves thus sent out from secondary sources along the slit are nearly in-phase when arriving any point in the forward direction. The diffracted wave resembles a circular wave with centre at the slit.

currently i think the ejs applet above only shows a circular source (i change it to n=1) at the slit width that spread in 180 degree which will occur when wavelength ~= slit width, that should be a lesser wave at the sides. i made slidth width = wavelength = 0.5, is should show lesser waves (represented perhaps by less intensity?) at the sides

A wave goes straight when the size of the slit is much larger than the wavelength.

currently i think the ejs applet above does not show this effect when wavelength << slit width



* diffraction.png (20.99 KB, 202x258 - viewed 446 times.)

* ejsslitwidthequalwavelength.png (343.92 KB, 785x704 - viewed 437 times.)

* diffractionwavefrontgoesstraight.png (587.3 KB, 791x701 - viewed 547 times.)
« Last Edit: January 31, 2011, 09:22:25 am by lookang » Logged
Fu-Kwun Hwang
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Reply #3 on: January 31, 2011, 03:42:06 pm » posted from:Taipei,T'ai-pei,Taiwan

I modified the above applet (add more constraints) so that it will be closer to the real case.

About your request to generate something similar to the following image.



Do you think the above image is a real wave? I am not so sure!

The intensity of diffracted wave should be much weaker than what has been shown in the above image.
And I do not think you will find any pattern (as found in the animation at http://ngsir.netfirms.com/applets/diffraction/2X/Diffraction.htm).

I will try to create one if you can show me a real experiment (video) which will generate pattern similar to the above image.  Wink
 
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Reply #4 on: January 31, 2011, 04:58:15 pm » posted from:Singapore,,Singapore

interesting suggestion!
i search the net and i found this

<iframe title="YouTube video player" class="youtube-player" type="text/html" width="480" height="390" src="http://www.youtube.com/embed/sjmBcm84iA4" frameborder="0" allowFullScreen>

time = 25 sec seems to suggest diffraction did not occur for a large slit width as the wave plane just travel through the slit as if there is no obstacle.


anyway, your ejs applet above, can already simulate a large slit i think.

simulation are models, the are close approximation of the real physics

i tried but like cannot get it because it is very lagging. i think i need to restart my PC.
i manage to change from interpolated to grid seems to run faster now.
and select n=8 source, n=100 is very lag for my PC.
i think the ejs applet model is close enough to the real life setup. Grin
not to worry then Cheesy



* diffractionreal.png (152.86 KB, 467x359 - viewed 459 times.)

* diffractionejs.png (109.41 KB, 672x626 - viewed 435 times.)
« Last Edit: January 31, 2011, 05:13:53 pm by lookang » Logged
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Reply #5 on: January 31, 2011, 06:15:44 pm » posted from:Taipei,T'ai-pei,Taiwan

You can use [sjmBcm84iA4] as forum message to display youtube video, where 'sjmBcm84iA4' is youtube movie id
( http://www.youtube.com/embed/sjmBcm84iA4 is the same as http://www.youtube.com/watch?v=sjmBcm84iA4 )


http://www.youtube.com/watch?v=sjmBcm84iA4
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