While the actual mechanics of choosing the equation

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Unformatted text preview: ccomplished by entering values into the legend of the graph. Click on the upper or lower legend value and enter a new value, then hit enter. If you cannot locate your data, you can select both "AutoScale Y-axis" and "AutoScale X-Axis" to let the program find the data for you. You can then adjust your axis scales to give you a convenient graph for analysis. Be careful, the AutoScale option will often set the scales in such a way that small fluctuations in the data are magnified into huge fluctuations. Data Fits Deciding which equation best fits your data is the most important part of using this analysis program. While the actual mechanics of choosing the equation and parameter is similar to what you did for your predictions, fitting data is somewhat more complicated. By looking at the behavior of the data on the graph, determine the best possible function to describe this data. After you have decided on the appropriate equation, you need to determine the constants of this equation so that it best fits the data. Although this can be done by trial and error, it is much more efficient to think of how the behavior of the equation you have chosen depends on each parameter. Calculus can be a great help here. This can be a time-consuming task, so be patient. Now you need to estimate the uncertainty in your fit by deciding the range of other lines that could also fit your data. This method of estimating your uncertainty is described in Appendix D. Slightly changing the values for each constant in turn will allow you to do this quickly. After you have computed your uncertainties, return to your best-fit line and use it as your fit by selecting Accept Fit in the Command Panel. Importing / Exporting Data After you have selected Analyze Data, it is possible to save your data to the computer's hard drive. This feature can come in handy if you need to analyze your data at a later date or if you want to re-analyze your data after you have printed it out. To save your data, simply select Export Data and follow the instructions in the windows. Your file should be saved in the LabData folder. To retrieve this file, restart MagnetLab from the desktop and select Import Data. 223 APPENDIX: SOFTWARE Last Words These directions are not meant to be exhaustive. You will discover more features as you analyze more data. Be sure to record these features in your lab journal. 224 APPENDIX: SOFTWARE FLUX SIMULATOR A computer movie called FluxSimulator shows the magnetic flux through a rectangular coil of wire (called a frame in the program). The frame is rotated in a uniform magnetic field changing the magnetic flux passing through it. The screen of this simulation is shown below. The magnetic flux is visualized by a “magic eye” that is always perpendicular to the crosssectional area of the frame (as shown below). The amount of flux "seen" is indicated by the use of color intensity as the frame rotates. Blue indicates positive flux while red indicates negative flux. Fr ame Magnet i c Fi el d Di r ect i on Fr ame' s Ar ea Vect or t hr ough Fr ame Fr ame Ey e' s v i ew of f l ux passi ng t hr ough f r ame Ey e Picture of FluxSimulator Screen Use the control bar with the slider, as shown below, to control the rotation of the frame. Slider As you rotate the frame, observe both the angle the frame's area vector makes with the magnetic field and the color seen by the eye. 225 APPENDIX: SOFTWARE VoltageTimeLAB - MEASURING TIME-VARYING VOLTAGES The Basics: This software package, written in LabVIEW™, allows you to measure and record potential differences as a function of time. The software and voltage interface act much like an oscilloscope. After logging into the computer, execute the application by double clicking the “VoltageTimeLab” icon located in the PhysLab folder on the desktop. Before you start using the program, you should take a moment to identify several key elements. The two most important of these are the Command Panel, shown to the right, and the Guide Box, shown below. The Guide Box will give you directions and tasks to perform. It will also tell you when to select a command in the Command Panel. You can also print and/or quit from the Command Panel or abort your analysis and try again. The primary data output you get is by generating pdf files of your results, so be careful not to quit without printing pdf files or exporting your data. Since the application to measure time-varying voltage is a slight modification of the application to measure magnetic field, you are already familiar with how to use much of it. The basic difference between the TimeVoltageLab and the MagnetLab applications is an additional display that is much like an oscilloscope. The potential difference versus time display is shown on the next page. The DAQ (Data Acquisition) control buttons are located directly above this display. The “DAQ START” and “DAQ STOP” buttons do as they suggest, stop and start data streaming from the probe to the voltage versu...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.

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