EMNG1001_Lab3_Current&Ohm'sLaw_InClass

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George Brown College Canada *

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EMNG1001

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Electrical Engineering

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Feb 20, 2024

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Student First Name: ……………………………………… Student Last Name: ……………………………………… Student Number: …………………………………………. Submission Date: ………………………………………… General Notes: 1. Type your name, student ID, and the submission date of the lab in the above fields. 2. Practice safety at all times. Carefully follow the directions of the lab. Do not use broken power cords or broken devices powered directly from the mains such as the DC supply. 3. Use only the electronic kit and devices provided by George brown college. Also, ensure that all equipment in the kit stays in good working condition. 4. Carefully read and follow ALL lab instructions provided in the lab write-up. 5. Complete all measurements, calculations, tables, drawings, and images required for all labs. 6. Answer all questions neatly and concisely in the spaces provided (preferably in bold red). 7. All Labs must be submitted by their due dates in Blackboard and cannot be made up. A grade of “Zero” will be assigned for missed labs. 8. The mark and possible feedback will be posted in Blackboard after the due date of each lab. Submission: This original word document with answers included in full is required to be submitted in Blackboard by the due date. It is not allowed to submit another separate document that includes only answers to the questions. Lab 3 Current and Ohm’s Law Objectives Upon completion of this lab the student will be able to: 1. Verify Ohm’s law by validating the relationship between voltage, current, and resistance. 2. Use the resistor color code to identify resistor values. 3. Use the digital multimeter to measure resistance, voltage, and current. 4. Estimate the power consumed in a resistor. Introduction George Simon Ohm theorized that there was a relationship between voltage, current, and resistance such that the circuit resistance ( R ) is directly proportional to the applied voltage ( V ) and inversely Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 1 EMNG1001 Circuit Analysis Lab 3 Current and Ohm’s Law

proportional to the current ( I ) flowing in the device. He discovered that for a given resistive circuit there was a fixed relationship between the voltage and current. This relationship can be expressed in equation form as: R = V I The power ( P ) consumed into a resistor due to the Ohmic losses can be determined from: P = VI = V 2 R = I 2 R In the previous lab, it was learned that the probes of the voltmeter have to be connected in parallel to the leads of the resistor to measure the voltage drop across it. In this lab, it will be learned that to use the multimeter as an ammeter to measure the current passing in a resistor the multimeter must be connected in series with the resistor. This is achieved by opening the circuit at the resistor and interconnecting the open ends with the multimeter probes. Part 1 Procedure 1. In this lab, the lab dual DC power supply is going to be used. Four different resistances will be powered from the DC source. Ohm’s law will be verified by measuring the voltage applied to each resistor and by measuring the current passing through it using the multimeter. It is important at the first step to know the maximum possible power consumed into the heaviest load used in the experiment. This is the smallest resistance R P,min that should be used in testing. Assuming the actual source voltage to be up to V s = 15 V and the maximum power rating of the used resistors to be P = 0.25 W , estimate the value of the smallest resistance to be used: R P,min = V s 2 P = ¿ ……………………………………… 2. Indicate the color code of the four listed resistors in Table 1. Take each of those resistors from the tools kit and measure its resistance ( R m ) using the multimeter set as an ohmmeter. Also, estimate the minimum ( R min ) and maximum ( R max ) possible resistances of each resistor in the table based on the manufacturer tolerances and the color-code resistance value ( R ): R min = ( 1 − tolerance ) R , R max = ( 1 + tolerance ) R The tolerance is 0.05 (i.e. 5%) for the gold tolerance band. Note: The resistances indicated in Table 1 are standard values and they should be included in the tools kit. However, if any resistance is found not available in the tools kit, then replace it with another closest possible value. Does the smallest chosen resistance in the table match the maximum power consumption of ¼ W? Answer [Yes/No]: ……………………………………… Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 2

Table 1 Resistance values and color codes. In d Required Resistance R (kΩ) Color Code Bands (1 st band – 2 nd band – 3 rd band – 4 th band) Measured Resistance R m (k  ) Minimum Resistance R min (k  ) Maximum Resistance R max (k  ) 1 1 2 2.7 3 5.6 4 10 3. Construct the circuit shown in Figure 1 using the breadboard, resistors, and short-link wires. The resistor in this figure should be connected to the variable DC power supply. Figure 1 Left: Circuit under test. Middle: Measuring voltage. Right: Measuring current. As a standard lab practice always connect the positive and negative terminals of the DC source to the circuit using the respective red and black wires with the alligator clamps. The left image in Figure 1 shows the circuit under test constructed on the breadboard. The DC source wires are always located to the left side in the figure images. Short circuit wire links are added to facilitate the measurement of voltage and current of the resistor. The middle image of the figure shows how to connect the multimeter as a voltmeter to measure the voltage drop across the resistor terminals. The voltmeter is shown connected in parallel with the resistor. The selector switch of the multimeter is set to the range of 20 V DC to function as a voltmeter. This selected range of voltage covers the DC source voltage. The right image of the figure shows how to connect the multimeter as an ammeter to measure the circuit current. The ammeter is connected in series with the resistor. Notice that the upper current shortening link has been removed to break the circuit at the position of engaging the ammeter. The selector switch of the multimeter, in this case, maybe set to the 20 mA DC range. Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 3

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4. Increase the DC supply voltage in a step of 2 V until a maximum of 12 V and each time using the procedure described in step 3 repeat measuring the voltage and current for all of the resistances in Tables 2-5. Using Ohm’s law estimate the value of each resistance: R Ohm' s = V s / I . Do not assume the source voltage to be constant in the different steps. Compute the percentage difference between the resistance estimated by applying Ohm’s law ( R Ohm ' s ) and the resistance that was measured using the ohmmeter ( R m ) of Table 1: %Difference = | R Ohm' s − R m | R m × 100% Table 2 Resistance values based on Ohm’s law for R = 1 k Ω . Required Source Voltage (V) Measured Source Voltage, V s (V) Measured Current, I (mA) Resistance, R Ohm' s (k  ) %Difference between R Ohm ' s and R m 0 0 0 N/A N/A 2 4 6 8 10 12 Table 3 Resistance values based on Ohm’s law for R = 2.7 k Ω . Required Source Voltage (V) Measured Source Voltage, V s (V) Measured Current, I (mA) Resistance, R Ohm' s (k  ) %Difference between R Ohm ' s and R m 0 0 0 N/A N/A 2 4 6 8 10 12 Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 4

Table 4 Resistance values based on Ohm’s law for R = 5.6 k Ω . Required Source Voltage (V) Measured Source Voltage, V s (V) Measured Current, I (mA) Resistance, R Ohm' s (k  ) %Difference between R Ohm ' s and R m 0 0 0 N/A N/A 2 4 6 8 10 12 Table 5 Resistance values based on Ohm’s law for R = 10 k Ω . Required Source Voltage (V) Measured Source Voltage, V s (V) Measured Current, I (mA) Resistance, R Ohm' s (k  ) %Difference between R Ohm ' s and R m 0 0 0 N/A N/A 2 4 6 8 10 12 Part 2 Questions & Answers 1. Using the data in Tables 2-5 plot the relation of the measured current taken as the vertical axis versus the measured voltage taken as the horizontal axis in the graph of Figure 2 for all four different resistors. Connect the measured points of each different resistor with straight lines (i.e. as one characteristic curve). You may replace Figure 2 with an image of the drawn graph or use Excel to draw the characteristics. Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 5

Figure 2 Plotting of I versus V s . 2. Explain the reasons for the possible differences between R m and R Ohm' s . ..................................................................................................................................................... ..................................................................................................................................................... ..................................................................................................................................................... 3. Which measurement method (ohmmeter versus the application of Ohm’s law) used in the testing has shown to be more accurate and more stable for verifying the resistances, or are they both sound to be the same? Use an argument in your explanation. ..................................................................................................................................................... ..................................................................................................................................................... ..................................................................................................................................................... Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 6

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4. Explain why do you think your testing results support Ohm’s law. Is the relation between current and voltage in the graph of Figure 2 sound to be linear for all tested resistances? Explain the reasons for the deviations from the ideal case. ..................................................................................................................................................... ..................................................................................................................................................... ..................................................................................................................................................... 5. What does the slope of each drawn characteristic curve in Figure 2 represent? ..................................................................................................................................................... ..................................................................................................................................................... ..................................................................................................................................................... Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 7