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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. UNIVERSITI MALAYSIA PERLIS 1 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. UNIVERSITI MALAYSIA PERLIS 2 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. UNIVERSITI MALAYSIA PERLIS 3 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 UNIVERSITI MALAYSIA PERLIS 4 DET101/3 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? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 2. In your own word explain what is Thevenin’s theorem? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3. In your own word explain what is Norton theorem? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4. Find the Thevenin’s equivalent circuit with respect to the terminal a, b for circuit shown below. UNIVERSITI MALAYSIA PERLIS 5 DET101/3 BASIC ELECTRICAL CIRCUIT I 5. Find the Norton equivalent circuit with respect to the terminal a, b for circuit shown below UNIVERSITI MALAYSIA PERLIS 6