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DET101/3
BASIC ELECTRICAL CIRCUIT I
EXPERIMENT 6
TITLE : THEVENIN’S AND NORTON THEOREM
OBJECTIVE
1. Compare between analyze of complex circuit and Thevenin/Norton equivalent
circuit.
2. Validate Thevenin’s theorem and Norton’s theorem through experimental
measurements.
3. Become aware of an experimental procedure to determine Vth, IN and Rth or
RN.
INTRODUCTION
The Thevenin equivalent method allows you to replace any circuit consisting of
independent sources, dependent sources, and resistors with a simple circuit consisting of a
single voltage source 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 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 circuit, 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 the following equation:
v oc  RTh i sc
(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 circuits containing only independent sources and
resistors, 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 isc.
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DET101/3
BASIC ELECTRICAL CIRCUIT I
EQUIPMENT AND PARTS
Digital Multimeter
DC power supply
Resistor
PROCEDURE
1. Construct the circuit in Figure 6.1. Insert the measured resistance values in Table 1.
2. Turn on the supply and set VS to 10 V and measure the voltage V L between terminal
x-y.. Using multimeter or Ohm’s Law, calculate the current IL. Insert the results in
Table 2.
3. Determine RTh/RN by replacing the voltage source with short circuit equivalent and
measuring the resistance with multimeter(Ω) between terminal x-y with RL being
removed as shown in Figure 6.2.
4. Determine VTh by constructing the circuit of Figure 6.3 and measuring the open
circuit voltage between terminal x-y with multimeter(V). Insert all results in Table 2.
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DET101/3
BASIC ELECTRICAL CIRCUIT I
5. Determine IN by constructing the circuit shown in Figure 6.4 and measuring the short
circuit current between terminal x-y with multimeter (A). Insert the result in Table 2.
6. Construct the Thevenin equivalent circuit as shown in Figure 6.5 using values
obtained in step 3 and 4 respectively. Use multimeter(Ω) to set the potentiometer
properly. Then measure the voltage VL and IL. Insert the values in Table 2.
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DET101/3
BASIC ELECTRICAL CIRCUIT I
RESULTS
Resistor
1k
2.2k
3.3k
470
Measure Value
Table 1: Measured resistor value
Parameter
Calculation
Experimental Result
Original Thevenin/Norton
Circuit
Circuit
Percentage Difference (%)
Original Thevenin/Norton
Circuit
VTh
RTh/RN
IN
VL
IL
Table 2: Thevenin and Norton electrical parameters, voltage and load current
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BASIC ELECTRICAL CIRCUIT I
EVALUATION QUESTIONS
1. In this experiment noting the overall results in Table 2, have Thevenin’s theorem and
Norton theorem been verified?
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2. In your own word explain what is Thevenin’s theorem?
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3. In your own word explain what is Norton theorem?
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4. Find the Thevenin’s equivalent circuit with respect to the terminal a, b for circuit
shown below.
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DET101/3
BASIC ELECTRICAL CIRCUIT I
5. Find the Norton equivalent circuit with respect to the terminal a, b for circuit shown
below
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