Physics 3LB_ week 3

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University of California, Irvine *

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3LB

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Electrical Engineering

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Dec 6, 2023

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Week 3: Meters and Ohm’s Law Equipment Oscilloscope DC Power Supply (PS) Digital Multimeter (DMM) Resistors (1kΩ ,10kΩ , 100kΩ and 1MΩ) Banana Cables (2 Red and 2 Black) 3.2.2 Ohmmeter Objective: The goal is to measure resistance with the DMM. The resistance reading is indicated through a mechanical meter movement which is operated on an electric current. It is only used when the unit is not connected to its original circuit. Description: The ohmmeter is an instrument for measuring electrical resistance. Resistance is expressed in ohms. The resistance is measured with the circuit's power turned off. The ohmmeter will send its own current through the unknown resistance and then measure the current to provide a resistance value. Data Analysis: Nominal Measured % Difference 1kΩ (DMM 2k) 0.997 kΩ 0.3% 10kΩ (DMM 20k) 9.98 kΩ 0.2% 100kΩ (DMM 200k) 99.6 kΩ 0.4% 1MΩ (DMM 20M) 1.00 MΩ 0% Conclusion: After trying different resistors we see a trend of that ohms measured are close and almost exact compared to the Nominal. With the use of the Digital Multimeter we can see the exact amount of resistance present. As well as % difference formula % = (Ω2 - Ω1 / Ω1) * 100 which supports

how similar the nominal resistance is to the measured resistance, which remained under 0.5%. Understanding how the Digital Multimeter measures resistance with no active current attached gives us range to how much will change when an active current is present in the circuit. 3.2.3 Voltmeter Objective: The goal is to measure voltage with the DMM. A voltmeter measures the difference in electrical potential, also known as the “voltage drop,” between two points in a circuit. Description: The instrument measures voltages of either direct or alternating electric currents on a scale using volts, millivolts or even kilovolts. The voltmeter can measure a voltage passing between two points because it is able to measure the difference between the positive and negative input voltages. It's commonly used to check power in electrical circuits. Place the internal meter on the power supply and set it on “voltage.” This will allow the P.S. meter and DMM to align. To measure the voltage with the oscilloscope, center the trace with the input disconnected to find 0 volts and then measure the deflection with the input connected. Data Analysis: Questions : 1. Does the DMM voltage give the correct voltage reading on the ACV scale? The DMM voltage and the ACV scale both show a value of about 5.21 V, therefore the DMM voltage does give the correct voltage reading on the ACV scale. This is only when the AC/DC switch is in the DC position. When the button is pushed in, the AC voltage, the DMM is at 0 but the ACV is still at about 5 V. 2. Measure the voltage with the oscilloscope too. The voltage per division is 5. When flipped to DC the line jumps up 5. When switched to AC the line does not move. There is no AC component, it is 0. DC Position GND Position AC Position No Image no graph created

Conclusion: We saw a positive jump on the oscilloscope when we moved from GND to the DC position. Since the power source is a DC Voltage we see the direct current produced on the Oscilloscope, being roughly 5 matching the voltage set on the Power supply. If there were an AC component present in the power supply the oscilloscope would reflect an AC setting. 3.2.4 Ohm’s Law Objective: The goal is to verify equation 3.1 : V=IR. The voltage across the material V is usually linearly related to the current that flows through the material, I. The constant R is the resistance and will depend mostly on the geometry and intrinsic properties of the material.The SI units are universal for the variables in Ohm’s Law. The V will be measured in volts, R will be measured with an ohmmeter to prove equation 3.1 and I with an ammeter. The ammeter will detect the current and is hooked in series with the resistor. The % variability between voltage of the power supply and IR is related with the following formula : (|IR-voltage|/Voltage) x 100. The resistance equivalence, Req = (Ri)(R1)/ (Ri+R1). For the % variability between V= IR and V = IReq, (|IReq - IR|/IR) x 100. Description: The power supply needs to be set to 5 volts. The current is measured with an ammeter in series with the circuit. The readings produced will be used to calculate the IR. In the following setup, the DMM is used as the ammeter, and the oscilloscope is used as a voltmeter. Data Analysis: Nominal Measured I V IR % Diff 1kΩ (DMM 2k) 0.997 kΩ 5.02 mA 5 volts/div 4.99 volts 0.2 % 10kΩ (DMM 20k) 9.98 kΩ 0.51 mA 5 volts/div 5.04 volts 0.8 % 100kΩ (DMM 200k) 99.6 kΩ 0.055 mA 5 volts/ div 4.98 volts 0.4% 1MΩ (DMM 20M) 1.00 MΩ 10 uA 5 volts/div 0.5 volts 90% IR Calculations: (.00502) x (997 x 1,000,000)/(997 + 1,000,000) = 4.99 volts (.00051) x (9980 x 1,000,000)/(9980 + 1,000,000) = 5.04 volts (.000055) x (99,6000 x 1,000,000)/(99,600 + 1,000,000) = 4.98 volts (.000001) x (1,000,000 x 1,000,000)/(1,000,000 + 1,000,000) = 0.5 volts % Difference Calculations:

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