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
2Jun11
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.
Prelab 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 twoterminal 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 opencircuit 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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View Full DocumentUniversity 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
2Jun11
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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 Summer '09
 Resistor, Electrical network, Thévenin's theorem, Norton's theorem, Current Source

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