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Easy Java Simulations (2001- ) => Optics => Topic started by: Fu-Kwun Hwang on January 28, 2011, 09:40:59 am



Title: Suposition of several waves
Post by: Fu-Kwun Hwang 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!  


Title: Re: Suposition of several waves
Post by: ahmedelshfie on January 28, 2011, 04:24:18 pm
WOW, i like too much  the design of applet.


Title: Re: Suposition of several waves
Post by: lookang 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.
(http://ngsir.netfirms.com/applets/diffraction/diffraction2.png)
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.(http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=2082.0;attach=3837;image) 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.
(http://ngsir.netfirms.com/applets/diffraction/diffraction1.png)
currently i think the ejs applet above does not show this effect when wavelength << slit width(http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=2082.0;attach=3839;image)



Title: Re: Suposition of several waves
Post by: Fu-Kwun Hwang 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.

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

(http://ngsir.netfirms.com/applets/diffraction/diffraction1.png)

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.   ;)
 


Title: Re: Suposition of several waves
Post by: lookang on January 31, 2011, 04:58:15 pm
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
(http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=2082.0;attach=3851;image)
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.  ;D
not to worry then  :D



Title: Re: Suposition of several waves
Post by: Fu-Kwun Hwang 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
( http://www.youtube.com/embed/sjmBcm84iA4 is the same as http://www.youtube.com/watch?v=sjmBcm84iA4 )

[youtube=sjmBcm84iA4]