LK-50A Resistances Voltages and Currents in S-P Combination Circuits - NEW

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Houston Community College *

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2126

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Electrical Engineering

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Dec 6, 2023

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LK-50 R – I – V IN SERIES-PARALLEL COMBINATION CIRCUITS - NEW 06/26/2022 OBJECTIVE 1. build a combination of series and parallel circuit with three resistors and one DC source. 2. Measure current passing through each resistor, and measure the voltage across each resistor. 3. Verify the equations of the combination of series and parallel circuit. EQUIPMENT AC/DC Electronics Lab Board Resistors Multimeter Voltage Sensor Current Sensor Two D-cells Wires THEORY Circuits combined by series and parallel wirings can be reduced into one equivalent resistance step by step. Each step is purely a series or parallel circuit. The circuit in the Figure 1 can be reduced into one equivalent resistance through two steps: R 2 and R 3 locally parallel equivalent to R 23 ; then, R 1 and R 23 locally series equivalent to R total . The resistance, current, and voltage relations for three resistors the circuit are the following: When resistances are placed in parallel, the total, or equivalent, resistance is given by the following equations: 1 R 23 = 1 R 2 + 1 R 3 ( 1 ) I 23 = I 2 + I 3 ( 2 ) ∆V 23 = ∆V 2 = ∆V 3 ( 3 ) R total = R 1 + R 23 ( 4 ) I total = I 1 = I 23 ( 5 ) ∆V total = ∆V 1 + ∆V 23 ( 6 )

Figure-1 The Current through one or a combination of resistors is given by Ohm’s Law: I = ∆V R (4) We will measure the resistance and voltage across the resistors and the current through the resistors, and compare these to the calculated values. The resistors are labelled by a color coding shown in Figure 2. We will set up the circuit on the AC/DC Circuit Board. A diagram with labels for different points is shown in Figure 3. Figure 2: Color Coding for Resistors. Figure 3: AC/DC Circuit Board with labels for different points. 1st Digit nd Digit 2 No. of Zeros Tolerance 0 1 2 3 4 5 6 7 8 9 Black Brown Red Orange Yellow Green Blue Violet Gray White None Silver Gold Red ± 20% ± 10% ± 5% ± 2% Fourth Band

PROCEDURE Better to select the same three resistors as were used for the Resistors in Series Lab. If they are not available, choose three resistors from those available. They may be of same or different values, but should range between 100 Ω to 1000 Ω (i.e. not smaller than 100 Ω and not larger than 1000 Ω). Refer to them as resistor #1, #2 and #3. Label them so that they don’t get mixed up. Determine the values of the resistances form the color code on them. Enter the Colors, Coded Value and Tolerance in Table 1. Use the Multimeter to measure the resistance of each of your three resistors. Determine the percentage experimental error of each resistance value and enter the values in the appropriate columns in Table 1. Use the measured values in all subsequent work. A- RESISTANCES IN COMBINATION 1. DO NOT attach the battery to the circuit. Connect the three resistors into the Combination Circuit, using the spring clips on the AC/DC Circuits Board to hold the leads of the resistors together. See Fig 4 for the circuit diagram, and Fig. 5 for the circuit on the AC/DC board (only a part of the board is shown). 2. Connect the Multimeter across C4 and C8. Set it up for resistance measurement. 3. In Fig. 5, the value of resistance that the Multimeters are showing are those of R1, R23 connected in parallel, and R123 connected in combination. Note these values in Table 2 as the measured values. 4. Use the measured values of R1, R2 and R3 from Table 1, to obtain the calculated values of R1, R23, and R123, as well as the percent errors. Figure 4: Circuit Diagram for resistances in Combination Figure 5: Diagram on AC/DC box

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