ECE 201 Fall 2008 Exam 2 October 28 2008 Division 0101 Clark 7 30am Division 0201 Elliott 10 30 pm Division 0301 Capano 3 30 pm Division 0401 Qi 4 30 pm Instructions 1 DO NOT START UNTIL TOLD TO DO SO 2 Write your Name division professor and student ID PUID on your scantron sheet 3 This is a CLOSED BOOKS and CLOSED NOTES exam 4 There is only one correct answer to each question 5 Calculators are allowed but not necessary 6 If extra paper is needed use back of test pages 7 Cheating will not be tolerated Cheating in this exam will result in an F in the course 8 If you cannot solve a question be sure to look at the other ones and come back to it if time permits 9 As described in the course syllabus we must certify that every student who receives a passing grade in this course has satisfied each of the course outcomes On this exam you have the opportunity to satisfy outcomes i iii iv and viii See the course syllabus for a complete description of each outcome On the chart below we list the criteria we use for determining whether you have satisfied these course outcomes Outcome i is a repeat We use this outcome result only if you did not satisfy it previously Course Outcome Exam Questions Total Points Possible i iii iv viii 6 9 1 4 9 14 5 28 28 42 7 Minimum Points required to satisfy course outcome 14 14 21 7 If you fail to satisfy any of the course outcomes don t panic There will be more opportunities for you to do so Potentially useful formulas are x t x x t o x e t t o L R 1 RC o 1 LC 1 Suppose that two experiments are performed on the circuit to the right and the results are tabulated below Experiment 1 Experiment 2 Vs 2V 1V Is 3A 1 A Iout 14 A 2A Then in the third experiment if we choose Vs 3 V and Is 1 A the output Iout in A will be 1 3 5 7 2 6 10 14 2 4 4 8 6 12 2 The current I in the circuit to the right is 1 2 3 4 5 6 7 1A 2A 3A 4A 5A 6A 5 A 2 3 Find the Thevenin equivalent resistance RTH for the network below 1 1 2 1 6 3 2 4 2 5 5 3 6 5 5 7 7 8 8 9 9 4 For the following network determine the short circuit current i e the current iA under short circuit condition at the terminals A B 1 90 mA 2 60 mA 3 40 mA 4 20 mA 5 0 mA 6 20 mA 7 40 mA 8 60 mA 9 90 mA 3 5 Find the maximum possible power transferred to the load resistor RL I1 2I1 4 12 V RL 1 6 W 6 144 W 2 9 W 3 18 W 4 36 W 4 5 72 W 6 The voltage vL t across an inductor L 4mH is shown in the plot below The current at t 0 is 0 Which plot best represents the current iL t through the inductor 5 7 In the circuit shown the voltage source is vs t 4 cos t V Then vL t is 2 3 cos t V 1 3 cos t V 3 6 sin t V 4 6 cos t V 5 4 sin t V 6 4 sin t V 7 12 sin t V ix vs t 2F vC t 0 25 H 3 ix vL t 8 Find the equivalent inductance of the network shown 6 1 1 H 2 2 H 3 3 H 4 4 H 5 8 H 6 12 H 7 16 H 8 24 H 9 Find the time constant in seconds for Vout t 1 1sec 2 2sec 3 3sec 4 4sec 5 5sec 6 6sec 7 7 sec 8 8sec 10 The following circuit consists of a switch and a step current source given by 2u t 1 A Determine the current iL t in A for t 1 second 1 2e 3 4e 2 t 1 1 t 1 4 3 5 8e 4 t 1 1 t 1 2 u t 1 u t 1 2 2e u t 1 4 u t 1 6 4e 4 t 1 u t 1 7 2e 2 t 1 u t 1 8 1 4 t 1 e u t 1 2 3 21 t 1 e u t 1 4 7 11 For the circuit shown the switch which has been closed for a long time opens at t 0 Which expression yields the voltage v t valid for t 0 1 5V e 5000t 3 5V 1 e 5000t 2 5V e 5000t 4 5V 1 e 5000t 5 10V e 5000t 7 10V 1 e 5000t 6 10V e 5000t 8 10V 1 e 5000t 12 For the following network determine i50 0 1 138 6 mA 2 100 mA 3 120 mA 4 37 5 mA 5 54 5 mA 6 200 mA 8 13 In a first order RC circuit excited by a voltage source the capacitor voltage is represented as vc t 4 6 e t 2 V Find the time in s required for the capacitor voltage to change from 8 V to 5 V Hint Recall that An a Anb An a b 1 2 ln 3 6 2 2 ln 4 3 4 ln 4 4 6 ln 13 4 5 2 ln 8 5 14 The switch changes from position 1 to 2 at time t 0 The angular frequency for vc t for t 0 is 2 1 2F 4H 1 rad s 16 1 rad s 4 2 7 4 rad s 1 2 vc t 2F 2V 1 rad s 8 3 1 rad s 4 5 1 rad s 6 2 rad s 8 8 rad s 9 16 rad s 9
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