http://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_principleHuygens[1] proposed that every point to which a luminous disturbance reaches becomes a source of a spherical wave, and the sum of these secondary waves determines the form of the wave at any subsequent time.
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Same Huygens-Fresnel principle Refraction on an aperture (slit) but notice the secondary source space equally apart and start from center ending 1/2 space from the edge of slit which is more logical than end at the edge of the slit. |
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Same Animation Huygens-Fresnel principle Refraction on an aperture (slit) |
Huygens assumed that the secondary waves traveled only in the "forward" direction and it is not explained in the theory why this is the case. He was able to provide a qualitative explanation of linear and spherical wave propagation, and to derive the laws of reflection and refraction using this principle.
http://electron9.phys.utk.edu/phys136d/modules/m9/diff.htm Diffraction is a phenomenon whereby waves appear to bend around obstacles, or appear to spread out after passing through a small orifice. The occurrence of
diffraction allows us, for example, to hear sounds from sources that are
hidden from us by some obstacle or other.
Diffraction is a wave phenomenon and is also observed with water waves in a ripple tank.
A wave spreads out (noticeable diffraction) when the size of the slit is comparable to or smaller than the wavelength. When wave passes through a small opening, comparable in size to the wavelength, in an obstacle (in this case yellow rectangles) , the wavefront on the other side of the opening resembles the wavefront shown below.
In the Ejs simulation case,
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when slit width is comparable in size to the wavelength |
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same animation when slit width is comparable in size to the wavelength |
The wave spreads around the edges of the obstacle (yellow in this case). This is the phenomenon of diffraction. Therefore, diffraction is "spreading out " wave phenomenon.
http://electron9.phys.utk.edu/phys136d/modules/m9/diff.htm has some photo of the real ripple tank.
in Ejs,I managed to capture a similar computational model.
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when slit width is comparable in size to the wavelength assuming 6 secondary sources, diffraction is noticeable |
I love Phet research and simulation
this is a great simulation called Wave Interference, under the water tab, the simulation breaks the 2D with a side view.
I managed to figure out a cool way to generate a 3D visualization is Ejs.
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when slit width is comparable in size to the wavelength assuming 6 secondary sources, diffraction is noticeable |
my favorable visualization is
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Spectrum visualization of when slit width is comparable in size to the wavelength assuming 10 secondary sources, diffraction is noticeable |
other interesting slit simulation are:
http://www.falstad.com/ripple/Contribution to benefit the world at wikimedia