BANGLADESH UNIVERSITY OF PROFESSIONALS (BUP)
DEPT. OF INFORMATION AND COMMUNICATION TECHNOLOGY (ICT)
COURSE: ICE 1104- ELECTRICAL CIRCUIT LABORATORY
Exp No: 05
Name of the experiment: Verification of Thevenin’s theorem in electrical circuit.
Objective:
To verify Thevenin’s theorem by determining the Thevenin equivalent voltage and resistance of a
given electrical circuit and comparing the theoretical results with the experimental measurements.
Theorem:
In electrical circuit analysis, it is often necessary to examine the impact of varying a specific branch
element while keeping all other branches and sources in the circuit unchanged. Thevenin’s
Theorem serves as a powerful analytical tool in such scenarios, significantly reducing the
computational effort required when changes are made to a particular element. According to
Thevenin’s Theorem, any two-terminal linear and bilateral network comprising
independent/dependent sources and passive elements can be replaced by an equivalent circuit
consisting of a single voltage source VTH in series with a resistance RTH. This equivalent circuit
behaves identically to the original network from the perspective of the two terminals under
consideration [1-3].
i.
ii.
VTH (Thevenin Voltage) is defined as the open-circuit voltage across the terminals A and
B of the network.
RTH (Thevenin Resistance) is the equivalent resistance seen from the same terminals when
all independent sources are deactivated (i.e., voltage sources are replaced with short circuits
and current sources with open circuits).
By reducing the original network to this simpler equivalent form, analysis of the circuit behavior—
especially with respect to changes in the load or branch connected across terminals A and B—
becomes much more efficient and straightforward.
Prepared by- Saiful Islam, Assistant Professor, Dept. of ICT, BUP
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Fig.1: Substituting the Thevenin’s equivalent circuit for a complex network [1].
Application notes and limitations of Thevenin’s theorem [4-7]:
Thevenin’s Theorem is widely used in electrical circuit analysis and design due to its ability to
simplify complex networks into a single voltage source and a series resistance. Its key applications
include:
a. Simplifying Load Analysis: Ideal for analyzing the behavior of a specific load resistor
when multiple sources and elements are present in the network.
b. Power Transfer Calculations: Useful in determining the load resistance that will receive
maximum power from the source network (maximum power transfer theorem).
c. Design and Testing: Enables efficient design iteration when components in one part of a
network need to be adjusted while keeping the rest of the network unchanged.
d. Troubleshooting and Fault Isolation: Allows engineers to focus on specific components
or branches by isolating them within a Thevenin equivalent circuit.
While powerful, Thevenin’s Theorem has certain limitations that must be considered:
a. Linear and Bilateral Networks Only: It is valid only for linear (obeying superposition)
and bilateral (same response in both directions) networks. Nonlinear or unilateral elements
(e.g., diodes) violate its assumptions.
b. Dependent Sources Handling: If the circuit contains dependent sources, calculating RTH
requires additional steps such as applying a test source at the terminals, rather than simply
deactivating sources.
c. Two-Terminal Restriction: Thevenin’s Theorem applies only to two-terminal networks.
For circuits with more than two output terminals, other techniques must be used (e.g.,
multi-port analysis).
d. AC Circuits with Reactance: In AC circuits with capacitors and inductors, VTH and RTH
become complex quantities (i.e., involve impedance), requiring phasor analysis.
Prepared by- Saiful Islam, Assistant Professor, Dept. of ICT, BUP
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Apparatus list:
a. DC Power Supply (0–30 V, adjustable) – 1 or 2 units
b. Resistors of known values (e.g., 100 Ω, 220 Ω, 470 Ω, 1 kΩ, etc.) – as required/available
in lab
c. Breadboard or circuit board – 1 unit
d. Digital Multimeter (DMM) – 1 or 2 units
e. Connecting Wires / Patch Cords – as required
f. Load Resistor (variable or fixed, to act as RL) – 1 unit
g. Switches or Jumpers (for easy source disconnection, optional) – as required
h. Wire Stripper/Cutter (optional, for preparing connections) – 1 unit
Circuit diagram (experimental set up):
IL
R2
A
A
S1
VS
R3
R11
RL
IL
1
V
VL
B
(a)
R2
VS
R11
IL
A
R3
A
RL
1
IL
V
VL
B
(b)
Fig.2: Experimental setup for verifying Thevenin’s theorem (a) with switches (b) without
switches.
Prepared by- Saiful Islam, Assistant Professor, Dept. of ICT, BUP
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Working Procedure (Based on Fig. 2(b)):
The following step-by-step procedure outlines the process of verifying Thevenin’s theorem for the
given network configuration:
i.
ii.
iii.
iv.
Construct the Original Circuit: Build the circuit as shown in the provided diagram, which
includes multiple resistors, one or more voltage sources, and a load resistor RL. Identify
the portion of the circuit (the “load”) across which the Thevenin equivalent will be found.
Measure the Load Voltage and Current (Original Circuit): With all sources active, measure
the voltage across the load resistor RL and the current flowing through it. Record these
values as the actual (original) circuit response in the corresponding data table.
Remove the Load Resistor: Temporarily disconnect the load resistor RL from the circuit to
allow calculation of the Thevenin equivalent. Draw and mark the circuit as Fig.2 (c).
Calculate the Thevenin Resistance (RTH):
A. Method 1 (Practical Measurement): Turn off all independent voltage sources (replace
with short circuits) and current sources (replace with open circuits). Then, measure the
equivalent resistance across the open load terminals using a multimeter—this is RTH.
Draw and mark the circuit as Fig.2 (d).
B. Method 2 (Theoretical Calculation): Alternatively, use circuit reduction techniques
(series-parallel combinations or star-delta transformations) to compute RTH
analytically.
C. Record these values in the corresponding data table.
v.
vi.
vii.
viii.
Determine the Thevenin Voltage (VTH): Build the original circuit and with RL removed,
measure the open-circuit voltage across the terminals where RL was connected. This
voltage is the Thevenin voltage VTH . Draw and mark the circuit as Fig.2 (e). Record the
value in the corresponding data table
Construct the Thevenin Equivalent Circuit: Rebuild the circuit using a single voltage
source VTH in series with a resistance RTHand reconnect the original load resistor RL across
the output terminals. Draw and mark the circuit as Fig.2 (f).
Measure the Load Voltage and Current (Thevenin Equivalent): Measure the voltage across
and current through RL in the Thevenin equivalent circuit. Record these values in the
corresponding data table.
Compare the Results: Compare the voltage and current values measured in the original
circuit with those obtained in the Thevenin equivalent circuit. If they match (or closely
agree), Thevenin’s Theorem is experimentally verified.
Prepared by- Saiful Islam, Assistant Professor, Dept. of ICT, BUP
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Data Table:
Table 1: Theoretical data for validation of Thevenin’s theorem.
Obs.
No.
VS
(V)
R1
(Ω)
R2
(Ω)
R3
(Ω)
RL
(Ω)
RTH
(Ω)
VTH
(V)
VL
(V)
IL
(A)
VTH
(V)
VL
(V)
IL
(A)
1.
2.
3.
Table 2: Experimental data for validation of Thevenin’s theorem.
Obs.
No.
VS
(V)
R1
(Ω)
R2
(Ω)
R3
(Ω)
RL
(Ω)
RTH
(Ω)
1.
2.
3.
Calculation:
Calculate RTH, VTH, VL, IL for the given values of voltage sources and resistors and verify the
theorem.
Discussion:
The discussion section should be developed independently, grounded entirely in your own
theoretical calculations and experimental observations. Provide critical commentary on the results
obtained, including any discrepancies or deviations observed. The use of external references or
AI-generated content is strictly prohibited. Non-compliance with these guidelines will result in
disqualification of the report from evaluation.
Experimental / Practical Questions:
1. Why do we remove the load resistor when calculating the Thevenin equivalent voltage
(VTH)?
2. How is the Thevenin resistance (RTH) measured practically in the experiment?
3. What is the significance of replacing voltage sources with short circuits while determining
RTH?
4. Why is it necessary to compare the current and voltage across the load resistor in both the
original and Thevenin equivalent circuits?
Prepared by- Saiful Islam, Assistant Professor, Dept. of ICT, BUP
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5. What might cause discrepancies between theoretical and experimental values when
verifying Thevenin’s Theorem?
6. How does building the Thevenin equivalent circuit help simplify complex circuit analysis?
7. What are the effects of loose connections or incorrect resistor values on the accuracy of
your experimental results?
8. What precautionary steps should be taken before measuring VTH and RTH in a real circuit?
9. Why must the measuring instruments (like DMM) have high accuracy and proper
calibration during the experiment?
10. In what situations would applying Thevenin’s Theorem be especially beneficial in realworld circuit design or analysis?
References:
[1] R. L. Boylestad, Introductory Circuit Analysis, 12th ed. Upper Saddle River, NJ, USA:
Pearson, 2010, ch. 9, sec. 9.2, pp. 345–353.
[2] J. D. Irwin and R. M. Nelms, Basic Engineering Circuit Analysis, 11th ed. Hoboken, NJ, USA:
Wiley, 2015, ch. 5, sec. 5.2, pp. 174–179.
[3] V. Del Toro, Electrical Engineering Fundamentals, 2nd ed. Englewood Cliffs, NJ, USA:
Prentice-Hall, 1994, ch. 3, “Superposition Theorem,” pp. approx. 13–19.
[4] A. Sudhakar and S. P. Shyam Mohan, Circuits and Networks: Analysis and Synthesis, 5th ed.
New Delhi, India: McGraw-Hill Education, 2015, ch. 4, “Network Theorems,” pp. 128–135.
[5] C. K. Alexander and M. N. O. Sadiku, Fundamentals of Electric Circuits, 6th ed. New York,
NY, USA: McGraw-Hill, 2017, ch. 4, sec. 4.3, pp. 120–126.
[6] W. H. Hayt, J. E. Kemmerly, and S. M. Durbin, Engineering Circuit Analysis, 8th ed. New
York, NY, USA: McGraw-Hill, 2012, ch. 5, “Thevenin and Norton Theorems,” pp. 165–172.
[7] Lecture notes and lab manuals commonly used in undergraduate electrical engineering
programs.
Prepared by- Saiful Islam, Assistant Professor, Dept. of ICT, BUP
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