Physics 134 Page

Physics 134 Page

new picture Data analysis portion of the final exam

Schedule for Section 1
Schedule for Section 3


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Fresnel Diffraction Analysis

A couple of years back I wrote an alternative to the MatLab program to allow students to see the straight-edge diffraction curves on the data as the fit is being set up and executed. In addition, the program calculates residuals and normalized residuals, which can help diagnose problems in the data.

I modified the original source on 2/9/00 to handle the case in Fresnel diffraction where the detector moves instead of the razor blade (you now have the choice). The source code for the fitting functions is available here:
Fraunhofer diffraction
Fresnel diffraction

The program runs on a Macintosh and can be accessed on Prof. Saeta's Macintosh (in the Physics Zone) using Appleshare and the Chooser:

  1. In the Apple menu select Chooser
  2. From the icon panel at the left, choose Appleshare
  3. Navigate the zones to HMC_Physics and to Saeta Office
  4. Use guest access
  5. Select ftp and click OK
  6. Now navigate the zones to HMC_Macs and choose KATO
  7. Select your class's partition on KATO and click OK

If this works according to schedule, you should have a folder named ftp mounted on the desktop and your class's KATO partition, which includes your folder.

Open the ftp folder, find the folder named Diffraction Fitter, and drag it to the desktop to copy it to the local hard drive. You may then drag the ftp folder to the trash, since you will be done with my drive.

  1. Prepare the data file: the program assumes a tab-delimited text data file. The file should have labels on the first row, and data underneath, as shown below.

    x (mm)  y (A.U.)    Error
    0.0     1.0         0.01
    0.25	2.5         0.02
    0.5     1.14        0.02
    

    A sample data file called Sample Data.txt is present in the folder, and you can use it to learn how to run the program. Sample output from the program using these data is shown below.

    You can use Kaleidagraph to help prepare the proper format text file, or a text editor such as Alpha or BBEdit (Mac) or some such program on the PC.

  2. Launch Diffraction Fitter. Then choose Fresnel Straightedge from the Function menu. A dialog opens; select your data file. The data will be displayed.

  3. The program assumes all distances are measured in mm, and that the dark region is at smaller values of x. Adjust the values of parameters by double-clicking on the number and typing a different value in the ensuing dialog. The new function is plotted over the data. Note that the Image Distance parameter has an "L" in the fourth column. This means that this parameter is locked (and will not be varied during fitting.) Change the 2000 mm value to the distance between the razor blade and the detector (in mm). You may also click the Chi Squared button to find out how you are doing.

  4. When you have adjusted the parameters to your satisfaction, click the Fit button. If all is well, you should see the program converge and the final value of Chi Squared updated.

  5. Do NOT print; you will crash. Instead, save the file. Then open the output in Kaleidagraph or other graphics program. It is tab-delimited text. It includes the original data, the fit curve, fit parameters and tolerances, chi-squared information, residuals, and normalized residuals.

Results

To make sure all is well, you can run the program on the supplied sample data file. The results, when gussied up in Kaleidagraph, should look like this:

FresnelDiffraction picture

Schedule for Section 1

ExperimentWeeks 1-3Weeks 4-6 Weeks 7-9Weeks 11-13
Experiment 1
Diffraction
Brad Forrest
Chris Wieland
Eric Brown Lara Mercurio
Kristi Hultman
Nicholas Breznay
Jimmy Corno
Experiment 2
Grating Spectrometer
Zach Walters
Lara Mercurio
Brad Forrest
Jimmy Corno
Eric Brown
Paul SanGiorgio
Chris Wieland
Kristi Hultman
Experiment 3
Lasers
Nicholas Breznay
Paul SanGiorgio
Chris Wieland
Zach Walters
Brad Forrest Lara Mercurio
Eric Brown
Experiment 4
Michelson Interferometer
Kristi Hultman Lara Mercurio
Nicholas Breznay
Zach Walters
Jimmy Corno
Brad Forrest
Paul SanGiorgio
Experiment 5
Fourier Transform Spectroscopy
Eric Brown
Jimmy Corno
Paul SanGiorgio
Kristi Hultman
Chris Wieland
Nicholas Breznay
Zach Walters

Schedule for Section 3

ExperimentWeeks 1-3Weeks 4-6 Weeks 7-9Weeks 11-13
Experiment 1
Diffraction
Curtis Vinson
Nigel Wright
Ozzie Osborn
Matthew Haddix
Mike Rust
Brian Kappus
Ben Schmidel
Marty Blood
Experiment 2
Grating Spectrometer
Seema Patel
Mike Rust
Nigel Wright
Marty Blood
Matthew Haddix Brian Kappus
Curtis Vinson
Experiment 3
Lasers
Ben Schmidel Curtis Vinson
Seema Patel
Nigel Wright
Ozzie Osborn
Mike Rust
Matthew Haddix
Experiment 4
Michelson Interferometer
Brian Kappus
Ozzie Osborn
Mike Rust
Ben Schmidel
Seema Patel
Marty Blood
Nigel Wright
Experiment 5
Fourier Transform Spectroscopy
Matthew Haddix
Marty Blood
Brian Kappus Curtis Vinson
Ben Schmidel
Seema Patel
Ozzie Osborn