Ejs Open Source Young's Double Slit Java Applet with double source and single slit option.
Young Double Slit Java Applet Ejs Open Source Physics Computer Model
author: andrew duffy and lookang, took some ideas from tat leong point P, Jose Ignacio Fernández Palop vcolor
original work here
many thanks to fu-kwun hwang for teaching me so many things on NTNU java forum
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the following text is from andrew duffy
Interference and Diffraction
With this simulation, you can explore the ideas of interference and diffraction resulting from waves passing through a single opening (the single slit); waves being emitted with equal amplitude in all directions from two sources (the double source), and waves passing through two closely spaced openings (the double slit). Note that the double-slit pattern is a combination of the single-slit and double-source patterns.
For the single slit that has a slit width a, the locations of the zeroes in the pattern (from destructive interference) are given by:
single-slit pattern, destructive interference: a sinθ = m λ, where m = 1, 2, 3, ...
For the double source, with a distance d between the sources, the locations of the zeroes in the pattern (from destructive interference) and interference maxima (from constructive interference) are given by:
double-source pattern, destructive interference: d sinθ = (m + 0.5) λ, where m = 0, 1, 2, ...
double-source pattern, constructive interference: d sinθ = m λ, where m = 0, 1, 2, ...
The double-slit pattern has the same equations as the double source,
double-slit pattern, destructive interference: d sinθ = (m + 0.5) λ, where m = 0, 1, 2, ...
double-slit pattern, constructive interference: d sinθ = m λ, where m = 0, 1, 2, ...
the commonly remembered formula could be sinθ = tanθ
therefore m λ / d = y / D
a check using m = 1, red = 0.64 x 10 ^-6 m, d = 4.1 x 10^-6 m, D =1.000 m, and indeed 0.156 = 0.156
with the exception of what are known as missing orders. This is when bright regions of constructive interference that are predicted by the last equation above are not observed, because they coincide with zeroes in the pattern associated with the single slit equation. When d/a = 4, for instance, bright lines corresponding to m = 4, 8, 12, ... (multiples of d/a) are missing from the pattern, because neither slit sends out waves in those directions.
activities suggested by andrew duffy
Different colors are associated with different wavelengths, which is why the patterns change when you change to a light source of a different color. Rank the colors red, green, and blue in terms of their wavelengths, from largest to smallest. With the single-slit pattern, what happens to the pattern when the width of the slit is increased? What happens to the pattern when the wavelength of the waves incident on the slit is increased? With the double-source or double-slit patterns, what happens to the pattern when the distance between the sources or slits is increased? What happens to the pattern when the wavelength is increased? For any of the patterns, what happens to the pattern observed on the screen when the distance to the screen is increased? Why? With the double-slit pattern, do you observe any missing orders? If the ratio of d/a (slit separation to slit width) is 4, for instance, do you observe missing orders for all bright lines corresponding to m = 4, 8, 12, etc.?