Midterm Exam for Linear Circuits - Winter 2009 | SOCC 140, Exams of Introduction to Sociology

Download Midterm Exam for Linear Circuits - Winter 2009 | SOCC 140 and more Exams Introduction to Sociology in PDF only on Docsity! MAE 140 – Linear Circuits – Winter 2009 Midterm Instructions 1) 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. 2) You have 70 minutes. 3) Write your name, student number and instructor. 1 A + − 10 10 V A C B 2i1i 20 ΩΩ Ω 20 Ω20 i3 D Figure 1: Circuit for questions 1-4. Questions 1. Equivalent circuits (a) (2 points) Turn off all the sources in the circuit of Figure 1 and find the equivalent resistance as seen from terminals A and D. Solution: First determine the circuit with all sources off: (1 point) D 10 A 20 ΩΩ Ω 20 Ω20 The equivalent resistance is then [(20//20) + 10]//20 = [10 + 10]//20 = 20//20 = 10 Ω (1 point) (b) (3 points) Find the Thévenin equivalent as seen from terminals A and D. Solution: The simplest possible way may be to use a source transformation on the current source to obtain the following circuit: (1 point) 20 V + − 10 10 V A 20 Ω Ω 20 Ω D − + 20 Ω Then associate the voltage sources in series: 20 − + 10 A 20 Ω Ω 20 Ω D 10 V Ω and apply a source transformation: (1 point) Ω 10 A 20 Ω Ω 20 Ω D 0.5 A 20 Associate 20//20 and perform one more source transformation: 10 − + 10 A Ω 20 Ω D 5 V Ω Calculate the open-circuit voltage VT directly using voltage division VT = 20 10 + 10 + 20 5 V = 2.5 V and use part (a) to draw the Thévenin equivalent: (1 point) D − + 2.5 V Ω10 A (c) (1 point) Find the power absorbed by a 10Ω resistor if connected to terminals A and D. Page 2