ELEC_315_Final_December_2019_coirrected

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University of British Columbia *

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315

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Electrical Engineering

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Dec 6, 2023

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Name: Number: Page 1 of 11 ELEC 315 Final December 2019 Closed Book. Only pens, pencils allowed. No calculators. Time: 120 minutes. Equation list and periodic table provided on last 2 pages. This examination consists of 11 pages. Please check that you have a complete copy. You may use both sides of each sheet if needed. Page # MAX GRADE 2 23 3 13 4 27 5 16 6 15 7 21 8 21 9 8 TOTAL 140 IMPORTANT NOTE: The announcement “stop writing” will be made at the end of the examination. Anyone writing after this announcement will receive a score of 0. No exceptions, no excuses. All writings must be on this booklet. The blank sides on the reverse of each page may also be used. Each candidate should be prepared to produce, upon request, his/her Library/AMS card. Read and observe the following rules: No candidate shall be permitted to enter the examination room after the expiration of one- half hour, or to leave during the first half-hour of the examination. Candidates are not permitted to ask questions of the invigilators, except in cases of supposed errors or ambiguities in examination-questions. Caution - Candidates guilty of any of the following, or similar, dishonest practices shall be immediately dis missed from the examination and shall be liable to disciplinary action: -Making use of any books, papers or memoranda, calculators, audio or visual cassette players or other memory aid devices, other than as authorized by the examiners.- Speaking or communicating with other candidates.-Purposely exposing written papers to the view of other candidates. The plea of accident or forgetfulness shall not be received. Student Number READ THIS

Name: Number: Page 2 of 11 1. (5) Imaginary permittivity can be used to help describe: (i) The effect of resistance in a dielectric True False (ii) Loss-related mechanisms True False (iii) Heat generating mechanisms True False (iv) Inductance related phenomena True False (v) Capacitive storage True False 2. (4) The dielectric constant of Barium Titanate (a crystalline compound of barium, oxygen and titanium) is an impressive 3000 at room temperature at 60 Hz, while diamond is 5.66. Explain. 3. (5) In diodes, breakdown is (right – wrong): (i) Always by Zener Breakdown. True False (ii) Occurs in reverse bias. True False (iii) Can be due to tunneling from the p-side Conduction True False Band to the n-side Valence Band (iv) Is usually due to avalanche breakdown in lightly doped True False pn-junctions. (v) Can be used for voltage regulation True False 4. (5) At a junction between two materials, energy levels are present on each side. For the following configurations, indicate whether electrons will on average move left or right (use arrows) or if the state is at equilibrium (double ended arrow): 5. (4) What happens to the potential energy of an electron as it becomes confined within some distance of the nucleus? (right – wrong): (i) It goes up as 1/distance. True False (ii) It goes down as -1/distance 2 . True False (iii) It goes down, but kinetic energy goes up. True False (iv) Radiation is released by orbiting electrons, preventing electron-proton anihilation. True False

Name: Number: Page 3 of 11 6. (5) The conductivity of an intrinsic semiconductor (circle best answer): (i) Decreases with increasing temperature because of the drop in number of carriers with increasing temperature. (ii) Increases at high temperature with increasing temperature because the number of free carriers goes up exponentially with temperature. (iii) At low temperatures, increases with increasing temperature as donors and/or acceptors are ionized. (iv) Can be unchanged or drop with increasing temperature in a certain range because ionization is complete and mobility is dropping. (v) Increases as temperature increases due to increasing number of carriers having a large effect than the dropping mobility. 7. (2) Water has a dielectric constant of about 80 at room temperature largely because of polarization that is: (circle one) (i) Interfacial (ii) dipolar (iii) orientational (iv) ionic (v) electronic 8. (3) a) On the plot, label the mechanisms associated with the three highest frequency transitions in dielectric constant. 9. (3) Two energy states sit 27.5 meV = kT ln(3) ABOVE the Fermi level. How many electrons will be found, on average , in these states?

Name: Number: Page 4 of 11 10. (6) A material is coated with metal on both sides to form a parallel plate capacitor of area, A , and thickness, d . A voltage, V , is applied. If the real part of the dielectric constant is  ’ r , and the imaginary part is 10 -3 times lower (  ’’ r =  ’ r / 1000), derive an expression for the rate of power loss at frequency,  . (2) In each charge/discharge cycle, what is the ratio of stored to dissipated energy? 11. (5) True or False? (right – wrong): (i) In paramagnetic materials the B field inside the material is REDUCED relative to the applied field due to the effect of the field on spins. (ii) In diamagnetic materials the B field is INCREASED relative to the applied field due to the effect of the field on orbiting electrons. (iii) Most materials are diamagnetic. (iv) The remnant magnetic field is the B field produced by a ferromagnetic material when no current or external magnetic field is applied. (v) The coercive field is the H-field needed to bring a magnet’s B field to 0. 12. (14) Sketch the band diagram of a PN junction under Forward Bias at an applied voltage, V A . Assume a band gap E g . In your diagram (a) Label the conduction and valence band edges, and (b) the Fermi level(s) . (c) Sketch the densities of carriers , d n /d E , d p /d E on both sides. (d) Label the n and p sides (e) Show the applied bias potential, e V A and (f) Indicate on which side the positive voltage is applied with a “+”.

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