Quiz 2 - October 17, 2007 MSE 182 — Quiz 2 Name: 1....

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Unformatted text preview: October 17, 2007 MSE 182 — Quiz 2 Name: 1. True/False The bandgap of a metal is greater than the bandgap of a semiconductor. True 0% 2 +5 All semiconductors have the same bandgap. True ® '01”; A field effect transistor uses mechanical force to move electrons True w @ In a semiconductor, a hole is the combination of an atom and an electron. True Semiconductors conduct better as the temperature is reduced. True If two materials have the same elastic modulus, they will both undergo plastic deformation at the same stress. True 9% Stress=Force2/Area True Depending on the phase, chocolate can be a liquid or solid at room temperature alse The lever rule only works for phases containing mixtures of solids and liquids True In the solid, some metals can dissolve other metals. False 9 2. Draw a stress vs. strain curves for the following materials on the SAME axis. Label your axis. A) Iron; B) polyethylene (a typical polymer); C) diamond. Indicate at what strain you expect each sam le to fracture (I am only looking for an estimate). '1; 7g!” '10 g #5 .. I ,fjfio/éa/ film; [or 54’”) ,3 may #3 ,)A6MVL1$ wron a] 7%r QK‘S J iron _,2_ "’0 flow on 3 01.950qu «‘04 diamond stress PE 0.01% strain <l% 200% ® 5 Given the phase diagram below, answer the following questions. For all parts, assume you start from a liquid of 70 Mole% MgO at 2800 OC, and cool it to 2600 0C E f 2880 26:00 2430 Tarpsrewe (ac) 2230 2230 a) What is the composition of the liquid phase? MgO: 60 mole % NiO: 40 mole % b) What is the composition of the solid phase? MgO: 80 mole % NiO: 20 mole % c) What percent of the material will be solid (Mole-%)? Apply Lever rule. 70 — 60 80—20 mole%solid = * 100% = 50m0le% d) Draw the expected morphology of the solid phase if the liquid has been rapidly cooled. L We accepted any reasonable picture. 4. In the box below each diagram, write the letter of the corresponding material. Black indicates states filled with electrons, grey indicates empty states, white indicates no states, black dots indicate filled dopant states, gray dots indicate empty dopant states. Energy gaps are in units of electron volts (not to scale). a N-type Semiconductor Metal b. g c. Pure Semiconductor @ d. Insulator e. P-type Semiconductor 00...... 26V IOOOOOOOO 26V i:| 3 P75 W! 5. What is the change in length of a cylindrical stainless steel rod, with a Young’s modulus of 200 GPa, if you apply a 20 kN force? The stainless steel rod is 1 meter long and has a cross sectional area of 1 cm2. 69 F (20E3)N 0'=—=———————7=2E7Pa A 2 1m ' lcm* lOOcm Al 0' 82—:— l E * AZ=W=ODOW (200 E9)Pa What was YOUR favorite chocolate? Using the terminology of Materials Science, WHY? We looked for use of Materials Science concepts/terminology in your answers. 7. Applying the concepts of electronic properties we discussed in class, describe how a light emitting diode (LED) works. Use the band diagram to illustrate the relevant key points. Key points: an electron in the conduction band combines with a hole in the valence band and loses energy in the form of light (typically in the visible wavelengths). The wavelength of the emitted light corresponds to the band gap energy of the semiconductor. CB hv Eg VB ...
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Quiz 2 - October 17, 2007 MSE 182 — Quiz 2 Name: 1....

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