LABORATORY MODULE
ENT 163
Fundamental of Electrical Engineering
Semester 1 (2006/2007)
EXPERIMENT 4: Thevenin’s and Norton’s Theorem
Name
:____________________________________________________
Matrix No.
:______________________
School of Mechatronic Engineering
Northern Malaysia University College of Engineering
ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
EXPERIMENT 4
Thevenin’s and Norton’s Theorem
1. OBJECTIVE:
1.1
To compare between analyze of complex circuit and Thevenin /Norton
equivalent circuit.
1.2
To learn concept of ideal current source.
2. PARTS AND EQUIPMENT:
2.1
Breadboard – 1 unit
2.2
DC power supply – 1 unit
2.3
Digital Multimeter – 1 unit
2.4
Wires
2.5
Resistor :
2.5.1
100 Ω resistor - 1 piece
2.5.2
470 Ω resistor - 1 piece
2.5.3
1.0 kΩ resistor - 1 piece
2.5.4
1.5 kΩ resistor - 1 piece
2.5.5
4.7 kΩ resistor - 1 piece
2.5.6
9.1 kΩ resistor - 1 piece
3. INTRODUCTION:
The Thevenin equivalent method allows you to replace any circuit consisting of
independent sources, dependent sources and resistors with simple circuit
consisting of a single voltage sources in series with a single resistor where the
simple circuit is equivalent to the original circuit. This means that a resistor first
attached to the original circuit and then attached to the simple circuit could not
distinguish between the two circuits, since the resistor would experience the
same voltage drop, the same current flow and thus the same power dissipation.
The Thevenin equivalent method can thus be used to reduce the
complexity of a circuit and make it much easier to analyze. A Norton equivalent
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ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
circuit consists of a single current source in parallel with a single resistor and can
be constructed from a Thevenin equivalent circuit using source transformation.
Thus in this section we will present a technique for calculating the component
values for a Thevenin equivalent circuit, if you want the Norton equivalent circuit,
you can calculate the Thevenin equivalent circuit and use source transformation.
There are three important quantities that make up a Thevenin equivalent
circuit, the open-circuit voltage, Voc, the short circuit current, isc and the Thevenin
equivalent resistance, RTh. In the Thevenin equivalent circuit, the value of the
voltage source is Voc and the value of the series resistor is RTh. In the Norton
equivalent, the value of the current source is isc and the value of the parallel
resistor is RTh but it is not necessary to calculate all three quantities, since they
are related by following equation:
Voc = RThisc
(1)
Thus we need to determine just two of these three quantities and can use
their relationship to find the third quantity, if desired. In circuit containing only
independent sources and resistor, our Thevenin equivalent method will determine
the values of voc and RTh. When a circuit also contains dependent sources we
will modify the method and determine voc and RTh.
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ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
4. PROCEDURE:
4.1
Thevenin’s Theorem:
4.1.1
Consider the circuit in Figure 4.1 .Find its Thevenin’s equivalent
circuit. Draw and label your circuit in Figure 4.3.
4.1.2
Build the circuit shown in Figure 4.1 on the breadboard mounted to
the bench top, using the DC power supply as vs. Once you have built
the circuit, set the value of vs to 10 V. Be sure to use the multimeter
to make sure the terminal voltage produced by the power supply is
as close to 10 V as you can get it.
Figure 4.1: Schematic diagram of circuits.
4.1.3
Measure and record the voltage across a-b terminal. This is
Thevenin equivalent circuit voltage, voc.
4.1.4
Remove DC power supply from the circuit and disconnect its
terminal. Measure resistance across a-b terminal. Record its value
as this is Thevenin equivalent resistance, RTh.
4.1.5
Calculate the voltage drop across RL using this formula below:
VRL= vocRL
(2)
RTh + Rl
4.1.6
Connect RL and DC power supply back to the circuit. Turn on the
power supply, measure and record the voltage across RL (a-b
terminal).
4.1.7
Repeat step 1 till 6 for circuit in Figure 4.2.
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ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
Figure 4.2: Schematic diagram of circuits.
4.2
Norton’s Theorem
4.2.1
Consider the circuit in Figure 4.1. Find its Norton’s equivalent circuit.
Draw and label your circuit in Figure 4.4.
4.2.2
Connect the circuit in Figure 4.1. Replace RL with ammeter
(multimeter) and make sure the polarity of ammeter is right. Turn on
DC power supply and record the current. This is the value of Norton
equivalent circuit current source, isc.
4.2.3
Calculate voltage drop across RL from equivalent circuit using
formula below:
VRL= iscRThRL
(3)
RTh+ RL
4.2.4
Connect RL to the circuit and remove ammeter. Turn on power
supply, measure and record the voltage drop across RL (a-b
terminal). Compare calculated VRL with measured one.
4.2.5
Repeat step 2 to 4 for circuit in Figure 4.2.
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Laboratory Module
Name :
______________________________
Matrix No :
______________________________
Date: ______________
5. RESULT:
5.1
Thevenin’s Theorem
For circuit in Figure 4.1:
Figure 4.3: Thevenin equivalent circuit for circuit in Figure 4.1
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ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
Name :
______________________________ Date : ______________
Matrix No:
______________________________
Table 4.1: Measured and Calculated Value for circuit in Figure 4.1
Parameter
Measured Value
Calculated Value
Voc
RTh
VRL
For circuit in Figure 4.2:
Table 4.2: Measured and Calculated Value for circuit in Figure 4.2
Parameter
Measured Value
Voc
RTh
VRL
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Calculated Value
ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
Name :
______________________________ Date : ______________
Matrix No:
______________________________
5.2
Norton’s Theorem
For circuit in Figure 4.1:
Figure 4.4: Norton equivalent circuit for circuit in Figure 4.1
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Name :
______________________________ Date : ______________
Matrix No:
______________________________
Table 4.3: Measured and Calculated Value for circuit in Figure 4.1
Parameter
Measured Value
Calculated Value
iSC
VRL
For circuit in figure 4.2:
Table 4.4: Measured and Calculated Value for circuit in Figure 4.2
Parameter
Measured Value
iSC
VRL
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Calculated Value
ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
Name :
______________________________ Date : ______________
Matrix No:
______________________________
6. EXERCISE:
6.1 Determine the value of Rth, Voc at a-b terminal and i for circuit in Figure 6.1.
Figure 6.1
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ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
Name :
______________________________ Date : ______________
Matrix No:
______________________________
6.2 The Thevenin equivalent resistance RTH for the network in figure 6.2 was 3.2
kΩ. Detail how this could be altered to 2 kΩ by using a single resistor placed
across terminal A and B. Calculate the value of the resistor that will
accomplish this. Will the Thevenin voltage change?
Figure 6.2
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ENT 163 - Fundamental of Electrical Engineering
Laboratory Module
Name :
______________________________
Matrix No:
______________________________
Date : ______________
7. DISCUSSION:
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8. CONCLUSION:
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