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 Author Topic: Suposition of several waves  (Read 17098 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
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 « Embed this message on: January 28, 2011, 09:40:59 am »

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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 wave_singleslit.jpg (53.4 KB, 510x511 - viewed 639 times.) Logged
ahmedelshfie
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 « Embed this message Reply #1 on: January 28, 2011, 04:24:18 pm »

WOW, i like too much  the design of applet.
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lookang
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http://weelookang.blogspot.com

 « Embed this message Reply #2 on: January 31, 2011, 08:56:21 am »

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 583 times.)  ejsslitwidthequalwavelength.png (343.92 KB, 785x704 - viewed 580 times.)  diffractionwavefrontgoesstraight.png (587.3 KB, 791x701 - viewed 704 times.) « Last Edit: January 31, 2011, 09:22:25 am by lookang » Logged
Fu-Kwun Hwang
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 « Embed this message Reply #3 on: January 31, 2011, 03:42:06 pm »

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

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.

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lookang
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 « Embed this message Reply #4 on: January 31, 2011, 04:58:15 pm »

interesting suggestion!
i search the net and i found this

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.
not to worry then

 diffractionreal.png (152.86 KB, 467x359 - viewed 566 times.)  diffractionejs.png (109.41 KB, 672x626 - viewed 548 times.) « Last Edit: January 31, 2011, 05:13:53 pm by lookang » Logged
Fu-Kwun Hwang
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 « Embed this message Reply #5 on: January 31, 2011, 06:15:44 pm »

You can use [sjmBcm84iA4] as forum message to display youtube video, where 'sjmBcm84iA4' is youtube movie id