Thevenins Theorem

1. Experiment
To Verify Thevenin’s Theorem
Electrical Engineering Department
Maulana Azad National Institute of Technology
Bhopal, MP, India - 462003

2. Objectives
1. Calculate thevenin voltage (Vth).
2. Calculate Thevenin resistance (Rth).
3. Verify Thevenin Theorem with theoretical values by comparing with observed values.

3. Apparatus Required
Fig. 1 Rheostat
a b c

4. Apparatus Required
Fig. 2 Voltmeter
Fig. 3 Ammeter

5. APPARATUS REQUIRED
S. N. Equipment Name Rating Quantity
1. DC Voltage Source 12 V 01
2. Rheostat 1) R1A=180Ω, R2A= 560Ω, R3A= 470Ω
2) R1B=1.8KΩ, R2B= 5.6KΩ, R3B= 1.2KΩ
04
3. DC Ammeter 0-20 mA 01
4. DC Voltmeter 0-20 V 01
Equipment’s ratings may vary as per availability in respective laboratories.

6. Thevenin’s Theorem
 Thevenin's theorem states that “in any two terminal, linear, bilateral network having a number
of voltage, current sources and resistances can be replaced by a simple equivalent circuit
consisting of a single voltage source in series with a resistance, where the value of the voltage
source is equal to the open circuit voltage across the two terminals of the network, and the
resistance is the equivalent resistance measured between the terminals with all energy sources
replaced by their internal resistances.”
dc
V
1
R
2
R L
R
3
R
A
B
Fig. 4
th
V
th
R
L
R
B
A
Fig. 5 Thevenin equivalent circuit

7. Circuit Diagram
dc
V
1
R
2
R L
R
3
R
C
D
A
B
Fig. 6

8. Procedure
1. Theoretically calculate the Thevenin’s voltage (Vth), Thevenin’s resistance (Rth) and load
current (IL).
2. Now apply dc voltage across terminals A-B , call this voltage as Vdc as shown in fig. 7.
3. Connect voltmeter across terminals C-D and measure voltage on voltmeter. This voltage is
known as open circuit voltage or Thevenin’s voltage (Vth) as shown in fig. 7.
Fig. 7
dc
V
1
R
2
R
A
B
D
C
th
V

9. 4. Disconnect supply at A-B and voltmeter through C-D.
5. Now short terminals A-B and connect multimeter across terminals C-D. With the help of
multimeter measure resistance between terminals C-D. This is known as Thevenin’s resistance
(Rth) as shown fig. 8.
6. Calculate Vth and Rth by theoretical calculations, the theoretical values and measured values of
Vth and Rth should be approximately equal.
Procedure Count.
1
R
2
R L
R
3
R
C
D
A
B
Fig. 8

10. Procedure Count.
7. Connect load resistor RL across terminals A-B and measure IL for applied dc voltage as shown
in fig. 9.
dc
V 2
R L
R
C
D
A
B
A
Fig. 9

11. S. No. Measured Value Theoretical
Value
Vth Rth Vth Rth
1 9.081 V 606.22 Ω
2 9.081 V 2562.16 Ω
3
4
5
Observation Table
% ERROR = ……………?…………..

12. Precautions
1. Wearing of shoes with rubber soles is desirable.
2. You should not work with loose garments on machines.
3. Familiarise yourself with shock chart instructions.
4. Do not touch any terminal or switch without ensuring that it is dead.
5. Do not work alone in the laboratory.
6. Keep away from all moving parts as far as possible.
7. Use sufficient long connecting lead, rather than joining two or three small ones because if an
joint is open , it could be dangerous.
8. While using electronic equipment, ensure that they are properly earthed.

13. 1. The theoretical values and measured values of Vth and Rth and IL are approximately equal,
hence Thevenin’s theorem has been verified.
2. If the average error has some value, then conclude that “the Thevenin is verified with ---%
error”.
3. Also record the probable reasons of the error.
4. Mention the precautions taken during the execution of the experiment.
Conclusion