ECE 201 Fall 2008 Final Exam December 20 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 Please clear any formulas text or other information from your calculator memory prior to the exam 6 If extra paper is needed use back of test pages 7 Formulas are given on the final page of this exam 8 Cheating will not be tolerated Cheating in this exam will result in an F in the course 9 If you cannot solve a question be sure to look at the other ones and come back to it if time permits 10 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 all outcomes 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 You only need to satisfy the outcomes once during the course so any outcomes that you satisfied previously will remain satisfied independent of your performance on this exam Course Outcome i ii iii iv v vi vii viii ix Exam Questions 1 2 4 3 7 10 17 5 8 19 24 7 11 14 19 21 21 22 23 6 24 12 13 Minimum correct answers required to satisfy the course outcome 2 2 2 2 3 1 1 1 1 1 1 A current i t in Amperes see Figure below passes through an arbitrary cross section of a wire What is the net charge q in Coulombs that passes through that cross section in the time interval 0 t 10 seconds 1 1 2 6 3 18 4 12 5 8 6 24 7 0 8 1 2 2 For the following network of resistors each of value R determine the equivalent resistance Req 1 1 R 8 2 1 R 4 3 3 R 8 4 5 5 R 8 6 3 R 4 7 7 R 8 8 R 9 9 R 8 10 9R 2 1 R 2 3 Determine the voltage Vb 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 4 Find Vs for the circuit below in V 1 10 2 20 3 30 4 10 5 44 6 60 7 0 3 5 We make a series of measurements of the voltage VAB between two terminals of a box containing an electrical circuit Each measurement is made by connecting a resister RL between the terminals and then measuring the voltage VAB Determine the Th venin equivalent for the network in the box RL 50 100 250 500 1 Vth 5V R th VAB 15V 20V 25V 27 3V 1 20 2 Vth 5V R th 20 3 Vth 15V R th 1 20 4 Vth 25V R th 20 5 Vth 15V R th 20 6 Vth 30V R th 30 7 Vth 30V R th 50 6 A variable resistor RL is connected to a current source 4A and parallel resistor 20 as shown Determine the maximum power that the resistor RL can absorb 1 10W 2 20W 3 40W 4 80W 5 120W 6 160W 7 320W 8 640W 4 7 In the following circuit the switch has been closed for a long time prior to t 0 but opens at t 0 Find VR 0 1 6V 2 4V 3 3V 4 2V 5 1V 6 0V 7 1V 8 2V 9 3V 10 4V 8 For the circuit shown find the time constant for the exponential time dependence of the voltage Vx t in seconds 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 26 5 9 Find the correct RL RC or RLC equation which describes the behavior for the variable of interest in the circuit below for t 0 Suppose i L 0 0A and vc 0 0V The switch remains open for all t 0 8 V 2 i L t k1 k 2 t exp t 4 A k1e 2t k 2e 4t A 4 vc t k1e t 4 k 2e t 2 V 1 vc t vc 0 exp t 3 i L t 5 i L t i L 0 exp t A 2 6 vc t k1 k 2 t exp t V 7 i L t e t A cos d t Bsin d t A 6 10 Find the differential equation for vc t Note v c t dvc t Hint apply KCL at the top dt node 1 v c t 2vc t vs t 0 5is t 2 v c t 2vc t vs t 0 5is t 3 v c t vc t vs t 0 5is t 4 v c t vc t vs t 0 5is t 5 v c t vc t vs t 0 5is t 6 v c t 2vc t vs t 0 5is t 7 v c t 2vc t vs t 0 5is t 11 For the circuit shown the two resistors have the same value R Find R in that yields a critical damping condition 1 0 3 2 0 6 3 0 9 4 1 2 5 1 5 6 1 8 7 3 8 4 9 9 10 12 7 12 Determine Vout for the following op amp configuration 1 15V 2 10V 3 6V 4 5V 5 0V 6 5V 7 6V 8 10V 9 15V 13 vin t is given in the graph The value of vout t at t 2 sec assuming vc 0 0V is in V 1 1 2 2 3 3 5 2 6 4 7 8 8 4 4 14 A sinusoidal voltage of effective value 5V is applied to the input terminals A B of the circuit inside the box shown As the frequency of the source is varied the effective value of the current is measured as shown in the plot Which of the following networks could be contained in the box 9 15 Element A in the following circuit is either a capacitor or an inductor Determine the impedance of this element ZA that causes the current I to lag the source Voltage by 45 1 1000j 2 500j 3 250j 4 50j 5 50j 6 250j 7 500j 8 1000j 16 Determine the phasor voltage VR 1 j5V 2 6 25 2 5j V 3 1jV 4 1jV 5 1V 0 6 2 5j V 7 j2 5V 10 17 Using KVL the phasor voltage Vs in volts is 1 3 4j 2 j 3 2 3j 4 4 3j 5 4 3j 6 3 …
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