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# exam3sol - EE 215 Practice Exam 3(As before this practice...

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EE 215 Practice Exam 3 May 29, 2001 (As before, this practice exam has not been controlled for time or dependency on prior answers.) Topics 1 (3 points) a. A device that converts from electromagnetic radiation to electrical values (voltage and current) is called a(n) __________________. b. In radar, the doppler effect can tell you the ______________________________. c. The range of frequency that can be sent over a channel is called ____________________. 2. (First order circuit with exponential forcing function). In the circuit of figure P2, the source has the form () < = 0 10 0 10 4 t V e t V t v t s a. Find the current i for t 0. b. Find the inductance needed so that 99% of the natural response of the circuit is complete in 100 ms. 3. (Second order circuit) a. Write the differential equation for the voltage v in the circuit of figure P3 in terms of i s , R, C and L. (Assume i s is constant for t 0.) b. Suppose that source current i s is not constant, but rather gives rise to a forcing function of the form 3sin4 t . Further, suppose values of R, C and L are chosen so the characteristic equation is 0 3 5 . 2 5 . 0 2 = + + s s . Write the form of the forced response. Find the coefficients of the forced response. c. If the characteristic equation of the circuit is 0 5 2 2 = + + s s , and the source is A t u i s = 1 , find the complete response of the circuit for t 0. Evaluate all coefficients. d. If the values of R, L and C are 20 , 10mH and 300nF, respectively, and the source is A t u i s = 1 , how much energy will be dissipated in the resistor during the time t 0? 4. Steady state AC circuit a. AC voltage measurements are taken on the circuit of figure P4. They are: v s = 120.V Figure P2 + - 100 mH 1 v s i Figure P3 i s R v + - L C

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v R = 82.0V v X = 87.6V Mystery component X is known (don't ask how!) to be a capacitor or an inductor. Does KVL hold? Explain. b. Using your parts kit, you insert a capacitor in series with X. v R goes down. Is X a capacitor or an inductor? Explain your answer. c. If X is an inductor (which might not be the answer to part b) of 10mH, and R is 100 , and you obtained the measurements in part a, what is the frequency of the source?
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exam3sol - EE 215 Practice Exam 3(As before this practice...

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