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

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.

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