Download Ohm's Law Experiment: Identifying Unknown Resistor and Verifying Its Value - Prof. Jaime D and more Lab Reports Electrical Circuit Analysis in PDF only on Docsity! Lab-in-a-Box Experiment 3: Ohm’s Law Name: _____ _____ Pledge: ____ _____ ID: ____________ Date: _________________ Procedure: V 1 D C = 9 R 1 1 k R 2 = ( R e d , B l a c k , B r o w n ) 0 A B D C Figure 1: Circuit for verifying Ohm's law. Analysis: 1. Identify the unknown resistor shown in Figure1. What value does the color scheme “Red Black Brown” stand for? Red = 2, Black = 0, and Brown means multiply by 10Ω so, 20 x 10 = 200Ω 2. Calculate the current ABI flowing through the unknown resistor and the voltage ABV across it. Since the circuit is in series, the voltage divided by the total resistance gives the current IAB . 9v/1200Ω = 7.5mA. Therefore voltage over mA. Therefore voltage over Vab is 1.5mA. Therefore voltage over V. 3. What is the purpose of the 1 kΩ resistor? The purpose of the 1 kΩ resistor is to lower the voltage. Measurements: 4. Construct the circuit shown in Figure 1 on your breadboard. Note that the 9V source is provided by the ANDY board. 5. Plug the black DMM probe into COM and the red probe into V. Set the switch to the lowest volts scale that will not overflow for the expected voltage. 1 of 3 6. Measure the voltage ABV across the unknown resistor. (See Section 2.5 for good technique.) Make sure your polarities are correct. Be sure to include your units! The voltage measured by the DMM was 1.481V at 2V resolution. 7. Disconnect the wire from the unknown resistor to ground (wire BC). 8. Move the red DMM probe from the “V” jack to the “mA” jack and set the DMM switch to the minimum full-scale value that will not overflow for the expected current calculated in step 2. 9. Measure the current, BCI , passing through the resistor by completing the circuit with the two DMM probes. To do this, place the red probe on node B and the black probe on node C. Review Section 2.5 for the proper technique for measuring current. Again, make sure your polarities are correct. The amps measured by the DMM were 7.42mA at 20A 10. Using Ohm’s law, find the resistance value of the unknown resistor. meas expt meas V R I 1.481V / 7.42mA = 199.6 Ω 11. Remove the resistor from your circuit. 12. Move the red DMM probe to the “R” jack and measure the resistance of the unknown resistor. The DMM measured the resistance of the resistor: 197 Ω 13. What is the percent difference between your experimentally determined resistance in step 10 and the measured resistance value found in step 12? meas expt expt 100% R R R |197 Ω -199.6Ω |/199.6 Ω * 100% = 1.3% 14. What is the percent difference between the experimentally determined resistance found in step 10 and the nominal resistance value found in step 1? nom expt nom R 100% R R |200 Ω - 199.6 Ω | / 200 Ω * 100% = 0.2% 15. Is the difference of the experimentally determined value in step 10 within 5% of the nominal value? Is the difference acceptable? Why or why not? The difference of the experimental value is within 5mA. Therefore voltage over % of the nominal value. The difference is acceptable due to the error range which was +/- 8% +/- 3 digits. 2 of 3
