LK-49A Resistances Voltages and Currents in Parallel Circuits-NEW

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Houston Community College *

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Electrical Engineering

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Dec 6, 2023

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IC-362 RESISTANCES, VOLTAGES AND CURRENTS IN PARALLEL CIRCUITS -NEW 07/18/2022 OBJECTIVE The purpose of this lab is to experiment with the variables that contribute to the operation of an electrical circuit, specifically the resistance, voltage and current in Parallel circuits. EQUIPMENT AC/DC Electronics Lab Board Resistors Multimeter Voltage Sensor Current Sensor Two D-cells Wires Capstone THEORY In this Lab we will study the effects on the values of the net resistance, voltage drops and currents when resistors are placed in parallel combination with each other. When resistances are placed in parallel, the total, or equivalent, resistance is given by the following equations: Resistors ∈ ¿ 1 R eq = 1 R 1 + 1 R 2 + 1 R 3 + … ( 1 ) I 0 = I 1 + I 2 + I 3 = I 4 ( 2 ) ∆V = ∆V 1 = ∆V 2 = ∆V 3 ( 3 ) 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. 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. 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

A- RESISTANCES IN PARALLEL 1. DO NOT attach the battery to the circuit. Connect the three resistors into the Parallel 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 Multimeter is showing is that of R1, R2 and R3 connected in parallel. Note this value in Table 2 as the measured value of R123. 4. Now take out resistance R 3 from the circuit. To do this, you may disconnect any one side of the yellow colored wire, i.e. at C3 or C4, or both sides. Now measure the resistances across C4 and C8 in the already connected Multimeter. This will be the resistance across R 1 and R 2 connected in parallel. Note this in Table 2 as the measured resistance for R12. 5. Reconnect R 3 , and take out R 2 (the red wire). Note and record the resistance for R1 and R3 in parallel (i.e. R13 in Table 2). 6. Re-connect R2, and take out R 1 (the blue wire). You now have R 2 and R 3 in parallel. Note this in Table 2 as R23. 7. Use the measured values of R1, R2 and R3 from Table 1, to obtain the calculated values of R12, R23, R13, and R123, as well as the percent errors. Figure 4: Circuit Diagram for resistances in series Figure 5: Diagram on AC/DC box B- VOLTAGES IN PARALLEL 8. In the circuit already made, add two D-Cells. Connect B2 and B3 so that the two batteries are now in series with each other. 9. Connect B4 to SW1, and SW2 to S4. Connect S8 to B1. The circuit should now be as in Figures 6 and 7 (without the Voltage sensors). 10. When the switch is pressed, the current will flow from the battery in the direction: B4 - SW1 - SW2 - S4 – S3 – S2 – S1. Then through R1, R2 and R3 to S5, S6 and S7 and then to S8 – B1. This completes the circuit. 11. Connect the Voltage Sensor to Capstone, and use it to measure the voltages V1, V2, V3 and V123 across R1, R2, R3 and R123 respectively, by connecting the Voltage Sensor at the points as shown by the green lines (of course, only one at a time, since there is only one voltage sensor). 12. In Table 3, enter the values of the resistances from Table 2, and the measured values of the voltage across these resistances.

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