PracticeExam2 solutions

PracticeExam2 solutions - ENME 350 Electronics and...

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Unformatted text preview: ENME 350 Electronics and Instrumentation I Fall 2010 Z§ Problem 1 [ pts] Short Answer. Include units! IRLC Vin=5005(377t) a. Find the equivalent impedance of the circuit above as seen by the voltage source Vin in terms of R, L, C, co. an“ 1N” @4'29) \ ._—-— a “NC =- J‘“ t 9,2“ 3., sim— "L" ‘WC. (owe +1? 4 J jn b. Given that IRLc(jco) = 0.167 A, find the voltage across the inductor L in phasor form given L = 100mH. , 4,? I l 2 EL :3wL : wL‘L‘ I7- : 317g vL (3‘8: IELQ<JW) ‘ EL Exam 2 Page 2 of 11 Prof D Barker ENME 350 Electronics and Instrumentation I Fe” 2010 c. In the circuit below, v(t) = 170cos(377t) V and i(t) = 1cos(377t) A. What kind of circuit element is X1? Circle your answer. d. What is the RMS value of i(t) = 1cos(377t) A? {Mufiohrx ( " Mk1— W H ‘9 ‘ __ an, ,. 4 rms I IE Exam 2 Page 3 of 11 (‘va Inductor Capacitor “flaw vawmw w ~~~~~~~~~~ w- xxxxx fl ( K Prof D Barker ENME 350 Electronics and Instrumentation I Fall 2010 Problem 2 Wpts]. A 9V battery is used to charge a supercapacitor CS which will be used to power a remote-controlled airplane. Assume the supercapacitor is fully discharged before connected to the battery Vc(t<0) = O and the switch closes at t=0. (0 9V battery A. (flpts) What is the supercapacitor voltage (Vc) a long time after the switch closes at t=0? Vc = 9 v afl'l'qr lawj IF‘WKQ— $'L'€'\'<7.\ ICC“: IODLS ‘tkfl. 09m [3 B. (flpts) How long will it take the supercapacitor voltage (Vc) to reach 8V? (Remember the time constant for an RC circuit is r=RC) Tsv= — lOQm<J§) = 11 s -t/i: U¢1 VH4 (\‘Q— \ Z:R<.: _1‘: 8:9 0— 2 #3 a “V? 9 ‘ —"=/'C at Q. 9 )Vi "t/z‘ t=—Z,lv\(’/9\)=. -10DH('/9): Exam 2 Page 4 of 11 Prof D Barker ENME 350 Electronics and Instrumentation | Fall 2010 (a C. (Zpts) You would like the capacitor C5 to charge as quickly as possible so that you can fly your plane. Will the capacitor charge faster if Rb > 10 or Rb < 10? Circle your answer. wder bMaJEr ‘hwvz, mutate-cut J 12C. Exam 2 . Page 5 of 11 Prof D Barker ENME 350 Electronics and Instrumentation I Fall 2010 253' . Problem 3 [Jfir pts]. Assume Vc(t<O) = 0 before the switch closes and that the switch closes at t=0. R=200§2 L=10mH‘ + C=1uF VC Vin=5v t=0 ‘9 A. (Kpts) Calculate the steady state value of Vc(t) after the switch closes. Vc(t9°°) = V , lIAAl/L<..{’or ‘0‘)an filmpwir 8 B. ’(Zpts) Assuming that the current resistor value results in a critically damped response, will the circuit become underdamped or overdamped if a smaller resistor is substituted? Circle your answer. Overdamped «WK km “Mum.” N M % (haul—er Pram 9‘64; G§\QM»\P‘\Aj C. (Hpts) Draw an example response (Vc vs. time) assuming a resistor value is chosen so that the circuit is underdamped. Use the steady state value for VC that you calculated in part A. VC Exam 2 Page 6 of 11 Prof D Barker ENME 350 Electronics and Instrumentation | Fall 2010 Problem 4 [25 pts]. You have built a new sensor, but it is picking up low frequency noise that is affecting your measurements. Unfortunately, it is 2am and you need to demo the sensor tomorrow morning. You have a large selection of resistors and one 10mH inductor in the lab that you can use to remove the low—freguency noise while allowing the high frequencies you are measuring to pass through normally. (Remember the time constantfor an RL circuit 1': L/R.) A. (5pts) Draw a circuit that will accomplish this task using one resistor (R) and one inductor (L). Clearly mark the input and output voltages Vin and Vout with plus and minus signs at the terminals. B. (10pts) Draw the magnitude portion of the Bode plot (piece—wise approximation) for the circuit you drew in part A. Label two different points (frequency in terms of R and L and magnitude) and any slopes. If you make a mistake on this Bode plot, more are included on the last page. Circle the Bode plot with your answer. IHGCOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . .. 40dB ......... ..; ..................... .g ......... H; ......... Hg ......... .. 20dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. lz/iEUDL- 2/0L 2 l 3 l0 0) OClB -———'—————:-———;W:;.mW—ile——> : g : : _20dB . . . . . , . . . . . . . . . . . . , . “(.3 . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -40dB . . , . . . . . . . . . . . . . . . . . . . . . . . . .. -60dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., l7, R %t 3 “J “ (H l ' fiflW H: \1-9- -—- ——--" ‘— ML . §1+(”L/ra\\1fl \i; '" 2m» “in {2+ 3‘0 Exam 2 Page 7 of 11 Prof D Barker ENME 350 Electronics and Instrumentation I Fall 2010 C. (10pts) Calculate a value for the resistor R that results in 60dB attenuation at co = 10 rad/s given the 10mH inductor you found. -éO‘AB 3m“ — moo ’3 k = U5 ~ ‘0 teal/s L=Om0l I" IDOOL Exam 2 Page 8 of 11 Prof D Barker ENME 350 Electronics and Instrumentation I Fall 2010 25' Problem 5 [ypts]. Answer the following questions for the circuit below. Assume Vin is a sinusoidal source with frequency co. Vout 00) A. (10pts) Find the transfer function HUw) = . f . VinUw) In terms 0 R, C, L, and 0) Vek'fi‘mfl¢,m “Mtgalgw' in. - «a - \)M Van," % + EL \lo WL in} c. - wz’ L. C. "g 1: l f ‘ 7mm... .3 WW .. UL R+TJQ+JWL ch. av“)ch +3®E¢ B. (5pts) Calculate |H(jco)| as (090. There is more than one way to derive this answer. IHUCD) lm-90 = Exam 2 Page 10 of 11 Prof D Barker ENME 350 Electronics and Instrumentation | Fall 2010 C. (5pts) Calculate |H(j(o)| as (090°. There is more than one way to derive this answer. 5 D. WWMS) What kind offilter is this? H'ijk (@193 T3} \ +136” ZNR avatar“ C8(*1v— Exam 2 Page 11 of 11 Prof D Barker ...
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