lab3_u11_Thms_Wheatsone

lab3_u11_Thms_Wheatsone - University of Florida Department...

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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Department of Electrical & Computer Engineering Ode Ojowu, TA Page 1/5 Revision 0 2-Jun-11 Lab 3: Theorems and the Wheatstone Bridge OBJECTIVES To reinforce and verify the concepts behind the Superposition, Thévenin’s, and Norton’s Theorems To introduce and understand the concepts behind maximum power transfer To understand the design and use of a Wheatstone bridge circuit MATERIALS The lab assignment (this document). Your lab parts. Pre-lab questions including Multisim. Graph paper. INTRODUCTION The Superposition Theorem A statement of the superposition theorem is that the total effect of independent sources in a linear circuit is the algebraic sum of the effects of the independent sources considered separately. In the application of this theorem, the effect of only one independent source is considered at a time. All other independent sources are eliminated by replacing them with short circuits if they are voltage sources and with open circuits if they are current sources . Thévenin’s and Norton’s Theorems The application of either Thévenin’s or Norton’s theorem allows the reduction of a complex two- terminal circuit into a simple equivalent circuit that has the same output characteristics as the original circuit; i.e., a black box . Thévenin’s theorem states that any linear two-terminal circuit, as in Fig. 1a, may be replaced by a Thévenin voltage source of voltage V Th in series with a Thévenin resistance R Th , as shown in Fig. 1b. This equivalent circuit will produce the same voltages and currents in any external circuit as does the original linear circuit. The Thévenin voltage V Th is the open-circuit voltage across the two node terminals of the original circuit, as shown in Fig. 1c. The Thévenin resistance R Th is the resistance “looking” into the two Figure 1 Thévenin and Norton equivalent circuits.
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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Department of Electrical & Computer Engineering Ode Ojowu, TA Page 2/5 Revision 0 2-Jun-11 Lab 3: Theorems and the Wheatstone Bridge terminals A and B , as shown in Fig. 1d, with all independent sources deactivated: all the voltage sources are replaced by short circuits, and current sources by open circuits. For Norton’s theorem, the equivalent circuit is a current source in parallel with a resistor of the same Thévenin resistance R Th , as shown in Fig. 1e. The current I SC of the current source is the current in a short circuit placed across terminals A and B , with a direction of A to B. Maximum Power Transfer In some circuits, maximum power transfer to a load resistor is desired. One example of such a circuit is in an audio system in which the load is the resistance of a speaker. It is desirable for the speaker to absorb the maximum power that the audio circuit can deliver. As shown in Fig. 2, the circuit delivering power to the load can, for analysis purposes, be replaced by its
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lab3_u11_Thms_Wheatsone - University of Florida Department...

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