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Unformatted text preview: Chem 124 Fall 2011 Dr. Neff Name: Computer #: 27 Partner: Conductivity: LED Experiment Instructions: Each person is to submit an individual report after performing the experiment. This report is due at the beginning of class on Tuesday November 8th . You are to fill in the appropriate spaces using Microsoft Word to create a clear and informative report. Be sure to keep your answers and graphs within the allotted spaces (some resizing may be necessary on your part). You will turn in a hard copy of this report. Part 1: Temperature Dependence of Resistance, R, of a Metal In the table below, record the results of your measurements of resistance for each temperature you recorded. Be sure to title your table appropriately. Chart 1 Temperature Effect on the Resistance of a Choke Coil Temperature Resistance ( ) Room Temperature 157.7 Cold Temperature 30.5 1. Describe what you observed, i.e., how does resistance change with temperature? Explain why resistance of a metal changes as it does with temperature. As seen in chart 1, the temperature decreased, the resistance decreased. This is due to the addition of heat energy, which, in turn adds kinetic energy. Since that is more kinetic energy, there are a greater number of electron vibrations. These electrons vibrating make it more difficult for the electrical current to flow. Part 2: Band Gap of a Compound Semiconductor LED: Effect of Composition In the table below, record the results of your observed values of voltage and color and your calculated values for the energy and wavelength. Be sure to title your table appropriately. Chart 2 The Effect of Phosphorus Substitution in GaAs on Voltage, Energy and Wavelength LED Composition P content, in % Measured Voltage Observed Color Energy, Joules Wavelength, nm GaP 1.00 As 0.00 100% 2.05 V Green 3.28 x 10-19 J 605 nm GaP 0.85 As 0.15 85% 2.94 V Yellow 4.22 x 10-19 J 422 nm GaP 0.65 As 0.35 65% 1.88 V Orange 3.01 x 10-19 J 660 nm GaP 0.40 As 0.60 40% 1.77 V Red 2.84 x 10-19 J 701 nm Chem 124 Fall 2011 Dr. Neff Show a sample calculation of each of the following: 1. Energy in Joules I V=1eV=1.602x10-19 J 2.05V x (1.602x10-19 J/ 1V) = 3.28 x 10-19 J 2. Wavelength in nm E=hc/ =hc/3.28 x 10-19 J = 605 nm In the space below, insert a graph of energy as a function of phosphorous content that you constructed using the data in the table above. the data in the table above....
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