Lab 2(2) (1)

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University of Alabama *

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225

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Electrical Engineering

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Feb 20, 2024

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ECE 225 Electric Circuits Laboratory LAB 2 – Ohm’s Law and Kirchhoff’s Voltage and Current Laws Objectives :  Learn how to build a circuit.  Learn how to use basic lab equipment to obtain measurements.  Verify Ohm’s Law, Kirchhoff’s Voltaage law (KVL) and Kirchhoff’s Current law (KCL).  Recognize the advantages and need to use modern tools to assist in solving problems.  Recognize some of the qualitative behavior/trends of voltages and currents in electric circuits. Pre-Lab: i. Perform Pspice simulations and theoretical analysis for the circuit shown in Figure 1 and find the voltage for each component and current through each branch. ii. Add a resistor in parallel with and find the voltage V o and the current Is. iii. Add a resistor in series with and find the voltage V o and the current Is. iv. Each student should submit a pre-lab report individually on the due date. Lab-Procedure: Import Notes:  Make sure that all sources are tuned OFF while building a circuit.  Ask the lab instructor to check your circuit connections and values before turning the sources ON.  Every time you modify a circuit or add/remove a measurement device from the circuit, first turn the sources OFF, make the necessary modification and then turn the sources ON again.  Carefully follow laboratory rules and safety rules given to you by the lab instructor. Equipment: Breadboard, Resistors, DC Voltage Source /DC Power Supply, Wires, and Digital Multi-meter. Prof. S. Kotru Lab2, Page 1 , Rev3 Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa.

ECE 225 Electric Circuits Laboratory Task 1: Building the Circuit Obtain the following components: , , , , , .  Measure and record the exact values of the resistors using the Ohmmeter function of the Multi-meter. Ask the lab instructor to help you on using the Ohmmeter function. Never measure a resistor value by the Ohmmeter while a resistor connected in a circuit, especially when there is a voltage source connected. Remove the resistor and measure its resistance if it is in a circuit.  Build the circuit as Shown in Figure 1. Remember the voltage source should be turned OFF. Figure 1  When you complete this task, ask the lab instructor to check your circuit before moving on to the next step. Task 2: Measurements 2.1 Voltage Measurements: Turn ON the voltage source.  Measure and record the voltages across each component using the voltmeter function on the multi-meter. The voltmeter should be connected in parallel between the two points where the voltage is to be measured.  Ask the lab instructor to help you make sure that your Voltmeter connections and setup are correct.  Do not forget to record the direction (sign convention) for each voltage. Prof. S. Kotru Lab2, Page 2 , Rev3 Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa.

ECE 225 Electric Circuits Laboratory  You should have a total of 6 voltages to measure and record. 2.2 Current Measurements:  Measure and record the current through each circuit branch using the ammeter function on the multi-meter. The ammeter should be connected in series with the branch where the current is to be measured.  Ask the lab instructor to help you make sure that your Ammeter connections and setup are correct.  Make sure to record the direction (sign convention) for each current.  You should have a total of 4 currents to measure and record. Task 3: Verify Ohm’s Law, KVL and KCL: Using the measured data (obtained in Task 2 and Task 3), do the following:  Verify Ohm’s Law ( or )  How do the calculated values of , and compare with the values you measured? If the values are different, explain the reason.  Apply KVL in each of the two circuit meshes using the measured voltages (obtained in Task 2). What do you notice and conclude?  Find the voltage V o .  Apply KCL at node “1” and node “2”. What do you notice and conclude?  What is the relationship between the currents in and and the current out of the voltages source? Explain? Task 4: Additional Tests  Connect an Ammeter in series with the voltage source.  Vary the voltage source (Vs) in steps (5V, 7V, 9V and 10V) and each time measure the source current (Is) and the exact source voltage. Prof. S. Kotru Lab2, Page 3 , Rev3 Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa.

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ECE 225 Electric Circuits Laboratory  Tabulate and plot the source voltage versus the source current. What do you notice in terms of the curve linearity? Why? How does the current vary (increase or decrease) and why?  Calculate Vs/Is value for each of the voltage and current readings in the previous step and add the results to the table. What do you notice in the resulting values each time? What does this value represent? How can you relate this value to the slope of the plot from the previous step?  Add a resistor in parallel with and measure the voltage Vo and the current Is. What happened to the values of Vo and Is and why? Discuss in detail.  Add a resistor in series with and measure the voltage Vo and the current Is. What happened to the values of Vo and Is and why? Discuss in detail. Task 5: Compare Results  For each task, compare the experimental and simulation results.  Calculate the percentage errors with respect to the experimental results.  Summarize these results in a table Task 6:  Discuss the benefits of having the ability to obtain computer simulation results. Task 7: Prepare a detailed report as per the guidelines provided and submit a lab-report on due date. Prof. S. Kotru Lab2, Page 4 , Rev3 Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa.