© 2014 IJIRT | Volume 1 Issue 6 | ISSN: 2349-6002
The validation of the Thevenin theorem
Sunil Sharma; Sooraj Chaudhary; Gautam kumar
Department of electronics and communication
DCE, Gurgaon, Haryana
current or across which you want to know the voltage. Label these
Abstract :-The validation of the Thevenin theorem is
terminals (where the resistor was removed) “a” and “b”.
presented in this paper. The Thevenin theorem was used to
Calculate the voltage across these open terminals. This is called
simplify the analysis of a complicated, resistive circuit driving
the open circuit voltage or the Thevenin equivalent voltage, VTH.
a resistive load. A resistive circuit was analyzed, simulated in
P-Spice, and built in the laboratory for verification of the
Thevenin theorem. Comparing the results from the analysis
and laboratory measurements, the Thevenin theorem was
verified with minimal percent error.
Thevenin’s Theorem:- In this experiment you will become
familiar with one of the most important theorems in circuit
analysis, Thevenin’s Theorem.
Thevenin’s Theorem can be used for two purposes:
 To calculate the current through (or voltage across) a
component in any circuit,
Or
 To develop a constant voltage equivalent circuit which
may be used to simplify the analysis of a complex circuit.
Any linear one-port network can be “replaced with” a single
voltage source in series with a single resistor (see Figure 1 below).
The voltage source is called the Thevenin equivalent voltage, and
the resistor is called the Thevenin equivalent resistance. What this
means is that a single voltage source and series resistor will
behave identically to the actual part of the circuit it is replacing.
In this experiment, you will use Thevenin’s theorem to solve a
complex DC circuit.
Step 2
From the open terminals, (“a” and “b”) calculate the resistance
“looking back” from the open terminals with all voltage sources
removed and replaced by their internal resistances (if RInternal = 0,
replace the voltage source with a short). This resistance is RTH.
Now we have the components we need to create the Thevenin
equivalent circuit as shown below using the Thevenin equivalent
voltage and resistance values calculated above connected in series
with the load resistor as shown below.
Figure 1 A network replaced with its Thevenin equivalent circuit
The steps used for Thevenin’s Theorem are listed below:
Step 1
Remove the resistor (R) through which you wish to calculate the
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© 2014 IJIRT | Volume 1 Issue 6 | ISSN: 2349-6002
Step 3
The current (through R) you wish to calculate will be:
IR 
VTH
R TH  R
VR  I R  
VTH R 
R TH  R
and the voltage across R will be:
where: VTH is from Thevenin
equivalent voltage obtained in Step 1, RTH is the Thevenin
equivalent voltage obtained in Step 2, and R is the value of the
resistor removed in Step 1.
Instructional Objectives
1. To work through the procedural steps involved in Thevenin’s
theorem.
2. To verify the values obtained by measuring them using the
digital multimeter.
3. To construct a Thevenin equivalent circuit.
Procedure:a) Connect the circuit in Figure 2. We will use Thevenin’s
theorem to find the current through R3.
Construct the circuit in Figure 3, and measure and record VTH.
VTH = ____________________________(meas)
e) Construct the circuit in Figure 4, which is the circuit in Figure
2 with R3 removed and the 12 V source replaced by a short circuit
(a dead voltage source). Calculate RTH in Figure 4, showing all
work.
Figure 4
RTH = _________________________(calc)
f) Verify your RTH calculation by measurement. Connect Figure
4, and measure and record the equivalent resistance (RTH)
measured between terminals a and b.
RTH = _________________________(meas)
g) Draw below the Thevenin equivalent circuit, using your
calculated values for VTH and RTH. This diagram is Figure 5.
h) Calculate IR3 using the Thevenin equivalent circuit (the VTH
I
Figure 2
b) Measure the current through R3 and the voltage across R3.
Record them:
IR3 =
__________________(meas)
VR3 =
___________________(meas)
c) You will now use Thevenin’s Theorem to calculate the current
through R3, by following the steps outlined in the introduction.
SHOW ALL WORK in the space provided. Record the results for
each step in the space provided.
Referring to Figure 3, which is Figure 2 with R3 removed,
calculate VTH in Figure 3, showing all work.
Figure 3
VTH = ________________________(calc)
d) Verify the actual Thevenin equivalent voltage by measurement:
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VTH
R TH  R 3
and RTH you found above)
i) Compare the current measured in step 1b (original circuit) and
the current calculated in step 3 above (which used Thevenin’s
Theorem). If they are not reasonably close, find the reason for the
discrepancy).
j) Build the circuit of Figure 5. Obtain a resistor for RTH as close
as possible to its calculated value (or use a potentiometer or a
decade box, whose value you can set equal to RTH).
k) Measure the current through R3 and the voltage across R3 in
the circuit of Figure 5. Record them:
IR3
=
_____________________(meas)
VR3
=
____________________(meas)
l) Compare these measured results with the results of part b (the
original circuit). If the results are not close, find the reason for the
discrepancy.
Figure 5
Conclusion:- Thevenin’s Theorem is a way to reduce a network
to an equivalent circuit composed of a single voltage source,
series resistance, and series load. Thevenin's Theorem is
especially useful in analyzing power systems and other circuits
where one particular resistor in the circuit (called the “load”
resistor) is subject to change, and re-calculation of the circuit is
necessary with each trial value of load resistance, to determine
voltage across it and current through it.
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