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3 Slit Grating
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A quick scan with a light sensor across a three slit diffraction pattern produced the above pattern. A He/Ne laser was used with wavelength 630 nm. The data for the experiment are contained in the initial conditions window of the Modellus model.
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The other animation window in the model shown below illustrates a single slit diffraction pattern as the slit width is changed.
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Change the width w2 and run the animation several times, observing the effect on the single slit above.
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Change w and s and look at the effect on the model calculation in comparison with the three slit data. Change the number of slits N in the initial conditions window to two and look at the pattern produced. Look at the 2 slit exam questions contained in the revision pack. Get a feel for how "w" and "s" affect the overall features of the grating pattern.
- Look at the cases for the single slit pattern shown above and make sure you can account for all the changes in the Intensity/Angle graphs.
Changing w and s, the slit width and slit spacing parameters for the model, will change the calculated pattern observed. Look at the diagram above.
- A "missing order" is shown in the picture above, produced by the model calculation. Explain how this occurred.
- Study the other cases and decide what was changed (look at initial conditions window in Modellus) to get a reasonable fit between the experimental data and the model.
- What is the connection between the single slit intensity pattern (for one of the three slits) and the general intensity pattern for the three slit grating? (Can you make an argument, putting the results of a simple three source interference model and single slit diffraction together to justify the features observed in the above experimental data?)
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Download this Resource
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Package:
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3slit.exe (126Kb)
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Contents:
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3slit.mdl, 3slit.doc and 3slit.bmp
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Instructions:
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Download the self extracting ZIP archive. Locate the file using Windows Explorer and double click. The self extractor will then start. The default installation path is C:\AP Revision. Having set the path press the Unzip button. After the files have been extracted change directory to C:\AP Revision. To start the model double click on 3slit.mdl.
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