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L11-12_AC_Circuits1-2

# L11-12_AC_Circuits1-2 - Physics 251 Laboratory AC Circuits...

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P251 AC Circuits Lab 1 Physics 251 Laboratory AC Circuits Part 1 - Implementation Pre-Lab: Please do the lab prep exercise on the web. Introduction This week we will set up a series RLC circuit driven by an ac voltage source, and use an oscilloscope and a digital voltmeter to study its behaviors. For reference, here are the equations we have discussed in lecture. V = V max cos( ϖ t ) I = I max cos( ϖ t - ϕ ) I max = V max Z Z = R 2 + X L - X C ( 29 2 tan ϕ = X L - X C R V L = I max X L cos ϖ t + π 2 V R = IR V C = I max X C cos ϖ t - π 2 P = I max V max cos ϕ 2 = I max 2 Z cos ϕ 2 = I max 2 R 2 You will be supplied with the following equipment: 1. Signal generator 2. Large coil with removable iron core 3. 4 μ F capacitor 4. Resistance decade box 5. Cables, clips, connectors, etc. 6. Oscilloscope 7. Digital voltmeter (DVM) Section 1 Set up the circuit as it is shown in the figure. Because of the way we will make measurements, it is important that the resistance box be “last” attached to the ground side of the signal generator . Initially, set the decade resistance box for 50 , and set the signal generator to produce a 2500 Hz sine wave. Set the amplitude of the sine wave to its maximum value. Do not use the iron core in the coil. Once everything is set up, do a few measurements. 1. Use the DVM to measure the voltage produced by the signal generator. 2. Set up the oscilloscope and look at the voltage waveform (measure at point A). Does the voltage you see agree with what the DVM said? V max cos( ϖ t) Coil 4 μ F Decade Box A B

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P251 AC Circuits Lab 2 3. Try varying the frequency and amplitude; make sure you understand what the oscilloscope is doing. 4. Now, move the DVM to measure the voltage across the resistor. Set the scope to measure at point B. Do these voltages agree? Should they? Section 2 In this section, we will measure the inductance of the coil both with and without the iron core in place. This can be done because we know the capacitance of our capacitor and we can measure the resonant frequency of the circuit. The amplitude of the current (and hence of V R ) is a maximum at resonance. 1. With the circuit set up as above, turn the frequency adjust knob all the way down (to 0.3) while stay- ing on the 1 kHz scale. 2. Measure the voltage across the resistor (point B) vs. the frequency all the way to the top of the scale. You may wish to “scan” the frequency range first and plan to take more closely spaced data near resonance.
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