### Author Topic: Suposition of several waves  (Read 17421 times)

#### Fu-Kwun Hwang

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• Posts: 3062
##### Suposition of several waves
« on: January 28, 2011, 10:40:59 am »
The following simulate suposition of several sinwaves (n=1-5).

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

Enjoy!

Full screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
• Please feel free to post your ideas about how to use the simulation for better teaching and learning.
• Post questions to be asked to help students to think, to explore.
• Upload worksheets as attached files to share with more users.
Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!

#### ahmedelshfie

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• Posts: 930
##### Re: Suposition of several waves
« Reply #1 on: January 28, 2011, 05:24:18 pm »
WOW, i like too much  the design of applet.

#### lookang

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• http://weelookang.blogspot.com
##### Re: Suposition of several waves
« Reply #2 on: January 31, 2011, 09:56:21 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

« Last Edit: January 31, 2011, 10:22:25 am by lookang »

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Suposition of several waves
« Reply #3 on: January 31, 2011, 04:42:06 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.

#### lookang

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• Posts: 1772
• http://weelookang.blogspot.com
##### Re: Suposition of several waves
« Reply #4 on: January 31, 2011, 05:58:15 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

« Last Edit: January 31, 2011, 06:13:53 pm by lookang »