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Unformatted text preview: MAE140  Linear Circuits  Fall 09 Midterm, November 10 Instructions (i) This exam is open book. You may use whatever written materials you choose, including your class notes and textbook. You may use a hand calculator with no communication capabilities (ii) You have 70 minutes (iii) Do not forget to write your name , student number , and instructor B + 10 V 0.5 A 10 40 20 10 A (a) Question 1. A v S i S B D C R 2 R 4 R 3 R 1 i 1 i 2 (b) Question 2. Figure 1: Circuits for questions 1 and 2. 1. Equivalente Circuits Part I [4 points] Use source transformations and association of resistors to find the Thevenin equiva lent to the circuit in Fig. 1(a) as seen from terminals A and B. Part II [4 points] A classmate was arguing with you that one would extract the most power out of this circuit by connecting a very small resistance between terminals A and B. You argued that he/she was wrong and that a 20 resistor would be a better choice. Who is right and why? Hint #1: Dont complicate: all you need to do is compare the two options! Hint #2: Use the Thevenin equivalent computed in Part I to answer the question. Solution: Part I: A possible series of source transformations is shown here: 10 V + + 10 V 40 20 A B 20 (+ 1 point) 20 V + 40 40 A B 40 A B 0.5 A 40 (+ 1 point) 0.5 A 20 A B (+ 1 point) + A B 10 V 20 (+ 1 point) Part II: Lets investigate the two scenarios. In the case of a small resistance, say R = , using the Thevenin equivalent and voltage division we have that...
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 Spring '10
 VladoLubarda

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