final_F07 - MatE 153 Fall 2007 FINAL Honor Code: I have not...

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Unformatted text preview: MatE 153 Fall 2007 FINAL Honor Code: I have not received any information about the questions on this test prior to the exam. During the exam, I will only utilize the provided material and a calculator. During the exam, I will not receive any information from fellow students. PRINT NAME: ____________________________ SIGNATURE : _____________________________ PARTIAL CREDIT WILL ONLY BE GIVEN IF YOU SHOW ALL YOUR WORK NEATLY!! YOU WILL LOSE POINTS IF YOU DO NOT INCLUDE THE UNITS!! 1 115 Points Total TOTAL _____ / 110 = _______ % 1.) Iron (Fe) is ferromagnetic. Explain why, when a liquid mould of Fe is solidified, the sample does not have a net magnetic field. (5 points) 2.) Describe what a built-in voltage is across a pn junction. Explain how/why it gets set up. (5 points) 2 3.) Make sketches on how n varies with 1/T for the three materials below. (10 points) 4.) Why is He2 unlikely? (5 points) 3 5.) You have an Fe (iron) metal wire at 600K. Assume that Fe has 4 valence electrons per atom. a. Calculate the mobility of electrons. (10 points) b. Calculate the Fermi energy at room temperature for Fe (5 points) 4 Part c is a continuation of the previous problem c. Draw the band diagram for that metal. Label on the diagram all the critical points including your calculated value from part b. (5 points) 6.) In a photoelectric effect, data is taken by shining light on a Au target. The target is then replaced with a Cs target (same light source in both experiments). a. Write an equation that relates the velocity of an electron freed from the Cs target (vCs) to the velocity of electron freed from the Au target (vAu). You do not need to solve your problem to get a numerical answer. (5 points) vCs = b. What is variable is measured (found from the collected data) in a photoelectric experiment that tells you the velocity of the freed electron? _______________________ (5 points) 5 7.) Assume that you have a electron trapped in a 1 μm sized well. What is the momentum of light needed to excite the electron from the first to third energy level? (10 points) 8.) In the lab where you measured optical absorption, what property of the semiconductor did you infer from the absorption edge? Why does absorption happen over an gradual transition region? (5 points) 6 9.) A Si sample is doped with 1020 atoms/cm3 of B (boron) at 300K. Calculate the a. Minority carrier concentration (5 points) b. Conductivity (10 points) c. Fermi energy (relative to the intrinsic Fermi energy) (5 points) 7 10.) Cobalt (Z=27) a. Give the 4 quantum numbers for each of the valence electrons (5 points) b. What is the estimated spin magnetic moment of a Co atom? (5 points) 8 Part c is a continuation of the previous problem c. If Co is the material used in generating the hysteresis loop below, what is the actual measured net spin magnetic moment of a Co atom? (10 points) 9 ...
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