Lab Report Isabel Cruz

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Electrical Engineering

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Jan 9, 2024

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Resistance and Ohm’s Law Lab Report By Isabel Cruz Lab Partner: Julius Davila Course: PHYS182-002-7 TA: Carter Eckel Due Date: 5:00 PM on 09/19/2023

Abstract For this lab we focused on resistance and ohm’s law. Our goals were to learn more about resistance and how it affects the electric current that flows through an object, use Ohm’s law to measure resistance, and predict and analyze how resisters in series and parallel behave when a voltage is applied. Our results showed us that for a device to be considered ohmic it has to have a constant resistance. Our predictions and actual data for the resistors in series and parallel was close which showed how we can add those resistances at different combinations. Our results for the relationship between resistance and length and diameter was not constant, however this was because of the device we used to measure the resistance. Introduction Our lab focused on resistance and ohm’s law. It was broken down into three parts. For the first part we focused on ohm’s law. We measured the voltage and current of a lightbulb, wire, and a diode to analyze their resistance and figure out if they were ohmic or not. To be considered ohmic, they had to have a constant resistance which is shown in the tables. If the data created a linear graph and went through the point (0,0) we considered it ohmic because the resistance was constant. For the second part we focused on measuring resistance. We used 5 different wires with different diameters but the same length for this part. First, we measured the resistance with a constant length and then with a constant area. We wanted to analyze their resistance and the relationship between the resistance and length. For the third part of the experiment, we predicted and calculated the resistance of several resistors combined in different ways. We analyzed them in series, parallel and a combination of series and parallel. This was to show us the different ways that resistors can be combined to produce different resistances. Theory In this lab we focused on Ohm’s law and the relationship between resistance, current, and voltage. We measured current and voltage and created a graph to show their relation and resistance. We calculated and analyzed how increasing length or diameter affected resistance. We also added resistors in series, parallel, and in combination. To see if an object was ohmic we analyzed resistance. Resistance tells us how hard it is for the current to flow through the object. Resistance is defined in voltage and current: R = V I where R is resistance, V is voltage, and I is current. This tells us how much voltage is needed for us to see the current flow. For an object to be considered ohmic, it must have a constant resistance. We used the equation for resistance to create a graph and analyze the linear equation for the different objects. If it was linear and had a point through (0,0) we considered it ohmic. Linear equations have a constant slope which in this case was the resistance. To analyze and compare how increasing length or diameter affected resistance we took measurements of the diameters, calculated the area, and measured the resistance. To calculate the area we used A = π r 2

where A is area, and r is radius. However, our device was not able to accurately measure the change in resistance, so we were not able to come up with a conclusion for their relationships. For the resistors in circuits, we added them. For the resistors in series, we added them. R series = R 1 + R 2 For the resistors in parallel we added them R ¿ = 1 R 1 + 1 R 2 The ones in parallel were lower because the resistors are lowering the voltage before going through the rest of the circuit and other resistors. Procedure In this lab we conducted a total of three different experiments with different parts. Our goals for this lab were to learn more about resistance and ohm’s law. For the first part we focused on ohm’s law. We measured the voltage and current of a lightbulb, wire, and a diode to analyze their resistance and figure out if they were ohmic or not. We took measurements of the current with different voltages. We needed 6 positive voltages and 6 negative voltages. To get a negative voltage we disconnected the resistor/voltmeter combination and reconnected them to the opposite terminal. We then used this data on excel to create a graph and analyze the linear function it created. We repeated this for the wire and diode as well. The data can be found on tables 1 to 3 and graphs 1 to 3. For the second part of the lab, we focused on measuring resistance with different diameters and lengths to see how length and diameter affect resistance. First, we kept the length at 20cm with different diameters to measure the resistance and calculate the area. Then we kept the area consistent by using just one wire and looking at the resistance at different lengths. The device we used was not able to measure the changes accurately so we could not conclude what the relationship between resistance and length and diameter was. The data can be found on tables 4 and 5. For the third part of the lab, we focused on adding resistors. We added them in series, parallel, and then in combination. We first took the measurements for the actual resistance of the resistors and predicted what they would be based on the equations stated above. We then measured their actual added resistance and compared. Results For this lab we focused on resistance and ohm’s law. Our goals were to learn more about resistance and Ohm’s law. We measured the voltage and current of a lightbulb, wire, and a diode to analyze their resistance and figure out if they were ohmic or not. To be considered ohmic, they had to have a constant resistance which is shown in the tables. The data in tables 1-3 and graphs 1-3 show our measurements and results for the voltages and currents we measured for the three different objects. The graphs for the light bulb and wire created linear functions between the current and voltage meaning that the resistance was constant. The data for the second part of the experiment did not give us accurate results because the device we used could not measure changes lower than 0.01 and our changes in resistance were small. The data for the third part showed that adding resistors in parallel loses voltage but adding them in series increases it.

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Conclusion and discussion In this lab we focused on Ohm’s law and the relationship between resistance, current, and voltage. We measured current and voltage and created a graph to show their relation and resistance. We calculated and analyzed how increasing length or diameter affected resistance. We also added resistors in series, parallel, and in combination. Our goals were to learn more about resistance and how it affects the electric current that flows through an object, use Ohm’s law to measure resistance, and predict and analyze how resisters in series and parallel behave when a voltage is applied. Our results showed us that for a device to be considered ohmic it must have a constant resistance. Our predictions and actual data for the resistors in series and parallel was close which showed how we can add those resistances at different combinations. Our results for the relationship between resistance and length and diameter was not constant, however this was because of the device we used to measure the resistance. This means that the change in resistance is not big when we change length and diameter but it does still change. To get accurate results, we would have to use a device can measure resistance at 0.01 and lower. Overall, we saw how ohm’s laws functions and how resistance affects it. Tables and Graphs Table 1 Lightbulb Current vs. Voltage Voltage (V) Current (I) 2.97 0.04 4.48 0.07 6.37 0.07 7.84 0.12 8.71 0.14 9.99 0.14 -1.84 -.0.02 -2.2 -0.03 -3.48 -0.05 -5.1 -0.08 -6.88 -0.1 -9.27 -0.13

Graph 1 Lightbulb Current vs. Voltage Table 2 Wire Current vs. Voltage Voltage (V) Current (I) 0.19 1.12 0.32 1.79 0.53 2.93 0.74 3.89 0.93 4.83 1.15 5.89 -0.16 -1.01 -0.24 -1.45 -0.45 -2.6 -0.68 -3.84 -0.92 -5.12 -1.12 -6.14

Graph 2 Wire Current vs. Voltage Table 3 Diode Current vs. Voltage Voltage (V) Current (I) 0.57 0.04 1.28 0.04 3.32 0.05 5.64 0.05 6.28 0.05 8.22 0.05 -0.39 0.05 -1.16 -0.05 -2.27 -0.02 -5.18 -0.01 -7.2 -0.19 -9.34 -0.26

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Graph 3 Diode Current vs. Voltage Table 4 Resistor Circuit Stated R (ohms) True R (ohms) % error 99.1 100 0.90% 199.5 200 0.25% 1015 1000 1.50% 10050 10000 0.50% 30670 30000 2.23% 972000 100000 2.90% Table 5 Constant I for wire at 20cm Diameter (cm) Area Resistance (ohms) 0.85 0.567 0.2 1 0.785 0.2 1.35 1.43 .2~.1 1.6 2.011 0.1 1.8 2.545 0.1 Table 6 Constant R for wire with .85cm diameter Length cm Resistance (ohms) 10 0.3

20 0.2 30 0.2 40 0.2 50 0.2 Table 7 Resistors in In Series Resistors Predicted Resistances (ohms) Measured Resistance (ohms) 100 100 102.9 200 200 193.9 100+200 In Series 300 296.7 100+200 in parallel 66.67 67.3 100+200 parallel, to 100 in series 166 165.4

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