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Unformatted text preview: University of California San Diego
Department of Electrical and Computer Engineering ECE 35 Practice Final Exam
Winter 2006 Name (Last, First) 2&3 Student ID number
I have neither provided nor received any assistance on this exam Signature 200 points total
This is a closed book exam — no notes of any kind are allowed.
You may use a handheld calculator, but not a laptop computer. You must show your work to receive credit on any problem. Write ciearly: work
which is not legible will not count towards your grade. All answers should be reduced to simplest form (decimal or fractions are OK).
Answers MUST HAVE UNITS to be correct (Le, 30, 2A, 4mV)
Write your last name on each page you hand in, including any extra pages
Good exam policy: (1) READ THROUGH THE ENTIRE EXAM BEFORE BEGINNING (2) WORK ON THE SIMPLER PROBLEMS FIRST (3) TRY TO ANSWER ALL PROBLEMS Problem 1: Resistor Codes Color code reminder
Black 0 Black
Beetles I Brown
Flunning 2 Fled 3 Orange cf Yellow
Green
Blue
Violet
Gray
Weather White What information is contained in the resistor color codes above? Answer: 20"”;le (2M3) 4157: Problem 2: Phasor notation Express the voltage function shown graphically below as (1) Atrigonometric equation: V07“ 0.3 '5‘“ 2174:" 041) V (2) An exponential equation: (3) Aphasor: O.B&'_2. +1V Ammo 08“  .._J a , vtt) 'A‘'A‘'A‘ Pew9.1 T = 3— = is
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 35 1V Last name 5““ Problem 3: Practical vs Ideal lab instruments
What are the performance characteristics of an "ideal” voltage supply? (1) Ideal: Can sapply legal1': Cuzruk‘l' ‘ho «min—lain Sci uniL13:
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(1) a common Alkaline battery, and
(2) the ACpowered voltage supply used in your lab Explain how the behavior of each of these is different from ideal.
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(3) ACpowered voltage source: No’r penccd'ltj sinblc
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Last name 5°I Pl Problem 4: Circuit analysis with OpAmps L1 z 39 Rq: E'ﬂ' 5 ‘3‘ Find Vout/ Vs for the circuit at right, FM“
assuming constant source voltage Vs
and ideal OpAmp behavior. 4:)
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identifying voltage, current. and resistance values. Find Vac. 107 aer‘jfﬁj KUL. On 105911,! —5V # lia‘Z‘id1'5ia =0 . _ §_ ia(1+5'7—1=5 =9 7’4’ “A
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P"? K: (itST 5' Lastname $oL'N Problem 6: Time response of RC circuit in the circuit at right, the first voltage source is always “on”
at V1 volts. while the second voltage source is switched
from 0 to V2,1 volts at time i=0. (1) Find the voltage across the capacitor, VG , for t<0
For {'— 4 0, 'HA! CtrCu'n'l' :5 '. " + . = V
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VI 9‘ " Vc. ‘ (2) Find vc ast—> no
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=>Vc(t>>°)=V.+V2_ l 9 (3) Write the time response Vc(t) for t>0, expressing coefficients in terms of the variables
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Vc (t) = (ViiV1) l [ \j .. (“H/AL /z,.c (3) Sketch v(t) for t>0. labeling important values Last name 5°91“ Problem 7: Time response of RC circuit For the circuit at right, (1) Write an expression for the total impedance
4 2: R +3'0L * a'uc. (2) Find the drive frequency w for which the impedance of the circuit 2 is purely real. ‘én'acc i=ﬁté(wL'Z§—é)i$ ma". ML” ”.3 (3) Given the drive voltage vd(t), sketch the steadystate voltage on each 9 as a function of time. Label the vertical axis in terms of the variablee; Last name SDL'N Problem 8: DC Circuit analysis Find the voltage of nodes labeled N1, N2 and N3 in the circuit below First, simplzLj flaﬂlud mais+brs N2
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: 2.5”]011 = 2.0. R
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V1(t) = 10Vcos(3t)
V2(t) = 5vsin(15t)
R: 10, C=(1/3)F, L= 1H
Sim—c. CJ‘ =3 ”f; fut: ISM/s
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TL: «ﬁnal urn«'4 ‘uue Sud. Q Pwuf‘M I Last name 50' '4 Problem 10: Transformers and maximum power transfer (1) Draw the Thevenin equivalent for the circuit below, assuming ideal transformer behavior 6mm cguaiiw'. so 2mF
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40‘1“!” the...) U #LeO‘VC a: vandalid. Last name Problem 11: AC Circuit analysis Find i(t) for the circuit below. Hint: solve using mesh currents COC = 1 '3 ﬂ  — Last name 5 ° ‘ '4 Problem 12: Lab circuits The circuit below is the band pass ﬁlter used in one of your labs.
Write the expressions for the two characteristics frequencies (high and low pass).
Hint: Don't derive the circuit equations, just write the simple equations from memory R2 1
l
(1”sz 2n E'c' (in HZ)
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(2) fLP = 2‘" K‘QL (in H2) Last name 50L“ ...
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