Physics 224 Lab 3 DMM

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California Baptist University *

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PHY224

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Electrical Engineering

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Apr 3, 2024

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Raquel Ibarra Christina Villanueva Section D 1/31/24 Physics 224L Lab #3: Circuits and the Digital Multimeter Purpose: The purpose of this experiment was to provide an introduction to circuits and to lay the foundation for future labs involving electrical systems. By engaging in tasks such as measuring resistance, voltage, and current using tools like the ohmmeter, voltmeter, and ammeter, participants gained hands-on experience in understanding the fundamental principles of electrical circuits. Through these measurements and observations, participants learned how components such as resistors and batteries interact within a circuit to control the flow of electricity and perform specific functions. Part 1: The Ohmmeter Task #1: Measure the resistance of 4 different resistors. Compare your measured resistance to the manufacturer’s color-coded resistance. color code resistance value measured resistance 2200 2160 330 331 1000 988 220 218 Question #1: Does it matter if you reverse the direction of the resistor when measuring its resistance with an ohmmeter? No, it doesn’t matter it provides the same exact number in the multimeter. Resistors are passive two-terminal components, which means they have the same resistance value regardless of the direction of current flow. Ohmmeters work by applying a small known

2 voltage across the resistor and measuring the resulting current flow to calculate the resistance. As long as the connections are made securely and the resistor is functioning correctly, the ohmmeter will measure the same resistance value regardless of its connected direction. Task #2: If each resistor below has a value of 100 ° , what does the ohmmeter read in each case below? The ohmmeter measure 33.2 for each of them. For the second picture the measurement is 98.8. Question #2: The measured resistance values should be different in the two cases in Task #2. Explain why. The two cases are different due to the three resistors sharing the total amount of ohms. The total is 98 however, it was split among three, so it is now around 30 each. The resistor that was shifted to the next row only was 98 because it was no longer connected/shared with other resistors. Therefore, the measured resistance values differ between the two cases in Task #2 due to the different configurations of the resistors within the circuit, either individually or in parallel, which influence the effective resistance seen by the ohmmeter. Question #3: What reading do you get when you connect the two ohmmeter leads directly to each other? What is the meaning of this reading and how does it affect your resistance measurements? What could you do to make your measurements more accurate? When you connect the two ohmmeter leads directly to each other, you typically get a reading very close to zero ohms or a negative value. This reading indicates the resistance of the leads themselves, along with any resistance introduced by the connection points and the internal resistance of the ohmmeter. W W 33.2 98.8

3 This reading means that the ohmmeter is measuring the combined resistance of its own leads and internal components. This resistance is usually very low, but not zero, hence the reading close to zero ohms. Task #3: Resistors in Series. Measure the equivalent resistance for 4 different combinations of resistors in series . 100 100 none 202 100 220 none 315 100 10,000 none 10,949 100 220 330 642 Question #4: How does the equivalent resistance of series resistors compare to the value of each individual resistor? Can you come up with an equation for adding resistors in series? Give a qualitative explanation for your answer. The equivalent resistance is the sum of all the resistors. An equation for adding resistors in a series is R equivalent =R 1 +R 2 +R 3. Qualitatively, this equation makes sense because the current flowing through each resistor is the same when resistors are connected in series. However, according to Ohm's law, the voltage drop across each resistor is proportional to its resistance ( V = IR ). As a result, the total voltage drop across the series combination is divided among the individual resistors. Since the voltage drop across each resistor depends directly on its resistance, the total voltage drop across the series combination equals the sum of the voltage drops across each resistor. Task #4: Resistors in Parallel. Measure the equivalent resistance for 4 different combinations of resistors in parallel . 100 100 none 99 100 220 none 136 ) ( R 1 W ) ( R 2 W ) ( R 3 W ) ( R equivalent W ) ( R 1 W ) ( R 2 W ) ( R 3 W ) ( R equivalent W

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4 100 10,000 none 196 100 220 330 168 Question #5: How does the total resistance of the parallel resistors compare to the value of each individual resistor? Can you come up with an equation for adding resistors in parallel? Give a qualitative explanation for your answer. The total resistance of parallel resistors is always less than the resistance of any individual resistor. This is because, in a parallel configuration, there are multiple paths for the current to flow, effectively reducing the overall resistance seen by the circuit. Mathematically, the equation for adding resistors in parallel is: 1/Requivalent= 1/R1+1/R2+1/R3 Where Requivalent is the equivalent resistance of the parallel combination, and R1, R2, and R3 are the individual resistance values of each resistor. Qualitatively, this equation makes sense because each resistor provides an additional path for the current to flow in a parallel configuration. As a result, the total current flowing into the parallel combination is divided among the individual resistors. Because each resistor offers its path for current flow, the overall resistance of the combination is decreased. Furthermore, because the total current flowing into the parallel combination is divided among the individual resistors, the effective opposition to the flow of current (resistance) is reduced when resistors are connected in parallel. This is why the total resistance of parallel resistors is always less than that of any individual resistor. Question #6: There are only a limited number of resistance values that manufactures produce. What would you do if you needed a different value for a particular application? When faced with the need for a resistance value that is not readily available among the limited options provided by manufacturers, there are several approaches one can take to achieve the desired resistance for a particular application. One standard method combines multiple resistors in series or parallel configurations to create a custom resistance value. For instance, resistors can be connected in series if a higher resistance value is needed, as their resistances add up. Conversely, if a lower resistance value is required, resistors can be connected in parallel, as their resistances decrease when combined in this manner. By selecting resistors with values that, when combined, achieve the desired resistance, one can effectively create custom resistance values tailored to the application's specific requirements. Task #5: Measuring the resistance of your body.

5 Measure the resistance of your body (from one hand to the other) by gripping the leads of your ohmmeter, one in each hand. Record your resistance value. measured resistance = 331 Mohms Question #7: Using the resistance of your body, determine what voltages it would take to produce each of the currents in the table below. For this, use Ohm’s law: V=IR Current Voltage 10mA can produce muscle contractions or muscle paralysis 3.31V 20mA can cause chest-muscle contractions interfering with breathing 6.62V 100mA to 200mA passing through your heart can cause ventricular fibrillation, usually leading to death 100 mA= 33.1V 200 mA= 66.2V Question #8: What is the resistance if your hands are wet? What danger does this pose to you? When your hands are wet, your skin's resistance decreases significantly compared to when it's dry. The exact resistance can vary depending on factors such as the amount of moisture present and individual differences in skin conductivity. However, when wet, your skin's resistance can drop to as low as a few kilohms or even lower. This decrease in resistance poses a significant danger, especially when dealing with electricity. When working with electrical devices or circuits, wet skin can result in a much higher current flowing through your body than when your skin is dry. This increased current flow can lead to electric shock, which can cause burns, tissue damage, cardiac arrest, and even death in severe cases. Part 2: Voltmeters Task #6: Measuring Voltage. From your ELVIS voltmeter measurements, what values did you measure for these batteries?

6 Task #7: Measuring voltages in series. What is the voltage of the combined batteries in series in each of the configurations below? Does the orientation of the battery matter? The orientation of the batteries does matter, we received different values when the orientation was changed. Question #9: When the voltmeter is connected to the circuit why isn’t the current in the circuit changed? Is the voltmeter connected in series or parallel? Battery 1 + + + - - - Voltage = 15.5 Battery 2 Battery 3 Battery 1 + + - - + - Battery 2 Battery 3 Voltage = 3.62 4.73 2.74 9.36 1.53

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7 When a voltmeter is connected to a circuit, it is connected in parallel. This means that the voltmeter is connected across the component or components for which voltage is being measured. The reason why the current in the circuit isn't changed when a voltmeter is connected is because the internal resistance of a voltmeter is very high. This high internal resistance acts as a large impedance in the circuit, allowing only a negligible amount of current to flow through the voltmeter itself. The voltmeter draws so little current that it has virtually no effect on the overall current flowing through the circuit. Since the voltmeter is connected in parallel, it measures the voltage across the component or components without significantly affecting the flow of current through the circuit. This allows for accurate measurement of voltage while minimizing interference with the circuit's operation. . Part 3: Ammeters Task #8 Measuring Current. Using the hand-held ammeter, measure the current in this circuit made of a 6V battery and a 100 ° resistor.

8 measured current = 56mA Question #10: Is your current measurement consistent with Ohm’s law, I=V/R? Calculate the expected current and compare to your measured value. Using Ohm's law, we can calculate the expected current: 6 volts 100 ohms=0.06 amperes I = RV =100 ohms 6 volts=0.06 amperes So, the expected current using Ohm's law is 60 mA. Given that the measured current is 56 mA, it is slightly lower than the expected value of 60 mA. This discrepancy could be due to factors such as the accuracy of the measurement equipment, variations in the actual resistance of the circuit components, or slight inaccuracies in the voltage source. Overall, the measured current is consistent with Ohm's law, albeit slightly lower than the expected value. Task #9 Measuring Current. Now using the ELVIS ammeter, repeat the current measurement of the circuit in Task #8. Do you get the same measurement values? Take a screenshot of the ELVIS ammeter and paste below. measured current = 59 mA 100 W mA

9 Question #11: When the ammeter is connected to the circuit why isn’t the current in the circuit changed? Is the ammeter connected in series or parallel? When an ammeter is connected to a circuit, it is connected in series. This means that the ammeter is placed in the path of the current flow and measures the current passing through the circuit. The circuit's current isn't changed when an ammeter is connected because an ideal ammeter has meager internal resistance. This low internal resistance effectively makes the ammeter act as a short circuit in the circuit path, allowing current to flow through it with minimal impedance. Since the ammeter is connected in series, it measures the current flowing through the circuit without affecting it significantly. The low resistance of the ammeter ensures that the voltage drop across it is negligible, allowing the current to continue flowing through the circuit uninterrupted.

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10 Conclusion: Through our experiment, we aimed to delve into the fundamentals of electrical circuits, using various measurement tools to understand their behavior. Our results aligned mainly with theoretical expectations, demonstrating the principles of Ohm's law, resistors in series and parallel, and the effects of wet conditions on electrical resistance. We successfully measured resistance, voltage, and current in different circuit configurations, achieving our primary goal of gaining hands-on experience with electrical systems. Overall, our results matched theoretical predictions. Resistance measurements correlated well with manufacturer specifications, and calculations based on Ohm's law were consistent with measured values. Additionally, our observations of resistors in series and parallel were in line with expectations, highlighting the predictable behavior of these configurations. However, discrepancies arose when measuring resistance with wet hands, as moisture significantly altered the results. This emphasizes the importance of environmental factors in electrical measurements. Our experiment successfully fulfilled its purpose of providing a foundational understanding of electrical circuits. We learned how to use measurement tools effectively, interpret results, and apply theoretical concepts in practical settings. The experiment reinforced the importance of accuracy and precision in electrical measurements and deepened our comprehension of circuit behavior. Additionally, ensuring calibration and proper handling of measurement equipment can minimize random errors and improve the accuracy of results. Overall, incorporating robust controls for environmental variables and equipment calibration can enhance the reliability and reproducibility of future experiments.