Ohm's Law-2

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Boise State University *

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111

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Electrical Engineering

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Apr 3, 2024

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Ohm’s Law The fundamental relationship among the three electrical quantities; current, voltage and resistance, was discovered by Georg Simon Ohm. The relationship and the unit of electrical resistance were both named for him to commemorate his contribution to physics. One statement of Ohm’s Law is that the current through a resistor is proportional to voltage across the resistor. In this experiment you will test the correctness of the law using several different circuits using the voltage and current probes connected to a computer through Vernier LabPro. Procedure 1. Using the power supply, connect the circuit as shown in the photo above, using a 10 Ω resistor, current and voltage probes. Connect the voltage probe to Ch 1 of LabPro and the current probe to Ch2. Set the power supply to 0 volts. 2. Open the Logger Pro experiment “Ohm’s Law” from the Phys 122 experiment folder. 3. Record the resistors rated value that is printed on the resistor in the data table. 4. Make sure that the voltage of the power supply is set to 0 V. Click the ‘Collect button’ in LogerPro to begin data collection. Monitor the voltage and the current. When the readings stabilize click the ‘Keep button’. 5. Increase the voltage by 0.5 V. When the readings stabilize click the ‘Keep button. Repeat this until you have reached 5.0 V. 6. Click the ‘Stop button’ and set the power supply back to 0.0 V. 9

7. Fit a linear regression line to the graphed data in LoggerPro and record the slope and the y intercept in the Data Table . Print a copy of the graph . 8. Repeat the above procedure (Steps 1 – 7) using a different resistor. 9. Replace the resistor with a 6.3 V light bulb. Repeat steps 1 – 7 except proceed with steps of 0.1 V up to 5.0 V. 10. To compare slopes of data at different parts of the curve, first click and drag over the first 3 points on the curve. Click the ‘Linear Regression button’ and record the slope in the table. 11. Click and drag around the last 10 points in the graph. Click the ‘Linear Regression button’ and record the slope in the Data Table. 12. Print the graph with both Linear Regression lines showing. Data Table Slope of Regression line (V/A) Y – Intercept (V) Resistor Ω - Yes 10.26 0 Resistor Ω - Yes 50.37 0 Light Bulb (first 3 pts) 42.8 -0.7 Light Bulb (last 10 pts) 71.63 -2.7 Analysis and Questions 1. As the potential across the resistor increased, the current increased. If the current is proportional to the voltage, the data should be in a straight line and should go through zero. In the case of the 2 resistors, how close is the Y-Intercept to zero? Is there a proportional relationship between voltage and current? If so write an equation for each in the form Voltage = constant x Current. (use a numerical value for the constant) The Y intercept is very close to zero, yet the current and voltage do not have a proportional relationship as although voltage may increase or decrease, current necessarily does not.

10 2. Compare the constant in each of the above equations to the rated resistance of each of the resistors. Calculate the percent difference for both resistors. The percent difference for both resistors is 0 %. 3. Resistance, R, is defined using R = V/I where V is the voltage and I is the current, and R is measured in ohms ( Ω ). The constant that you determined for each resistor should be close to the stated resistance printed on the resistor. However, resistors are manufactured such as that their actual values are within a tolerance of 1%, 5%, or 10% etc . The resistors used in this lab have a rated tolerance of 1%. Are your constants within that 1% error tolerance. Both resistors were within 10 percent error tolerance. 4. Do your resistors follow Ohm’s Law? (Based on your experimental data) Yes both, resistors follow Ohm’s Law.

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5. Describe what happened to the current through the light bulb as the voltage increased. Was the change linear? Since the slope was of the linear regression line is a measure of the resistance, describe what happened to the bulbs resistance as the voltage increased. Since the bulb gets brighter as it gets hotter, how does the resistance vary with temperature? The change was linear as temperature increased so did the resistance. 6. Does your light bulb follow Ohm’s Law? (Based on your experimental data) No, the light bulb does not realy follow ohms law as the resistance changes which mean it is not a contant which leads to the conclusion of not following Ohms law.