# Physic Lab

Lab AC circuits[footnoteRef:1] [1: Adapted from https://phet.colorado.edu/en/contributions/view/5011, RLC circuits by Eric Roebuck]

Use the following PhET simulation to complete the experiment. Include this document, figures in your submission.

Lab Goals:

To find the frequency of resonance of a RLC series circuit.

To study the phase shift between two signals.

To investigate power in AC circuits.

Part 1 – RLC Circuit

1. Create a circuit with an AC Voltage (source)in series with a resistor, inductor, and capacitor.
2. Right click the AC Voltage and click Change Voltage and note the current value of the voltage. Click Change Frequency and note the current value of frequency.
3. Place Voltage Chart around each element in the circuit, include the AC Voltage. Make sure the polarity is consistent. Take a screen shot an insert here.
4. Mark the maximum/minimum voltage on each graph. Qualitatively note the similarities and differences between the graphs. Which graphs are in phase with one another? Which graphs are not? What about the sign of the amplitude? You can easily do that by pressing the stop button.
5. Using the RMS voltages (VRMS = V0 / √2) show that the RMS voltage on the AC Voltage is consistent with the voltage sum of each element VRMS = √ [ (VRMS,R)^2 + (VRMS,L -VRMS,C)^2 ].
6. Using the resistance, capacitance, inductance, and the frequency of the AC Voltage calculate the impedance Z. By right clicking on each element you can find the values for each component. You don’t have to change the current values but if you click on change value it will display its magnitude.
7. Place a Current Chart after the battery in the circuit. Note the maximum value of the current. Using the RMS current show that the RMS voltage from the AC Voltage is consistent with the RMS current and impedance.
8. Change the frequency of the AC Voltage to the resonant frequency and click Reset Dynamics. Allow the simulation to run for at least one minute to adjust. Repeat steps #4-7. What similarities and differences do you see between the two tests. Screen grab your circuit and include the picture in your lab report. Save the circuit for your own records.

Part 2 – Average Power

1. Create an RLC circuit with resonant frequency of your own choosing. Initially set the resistance to 10 Ω. For at least 7 values of frequency fill out the table below. Make sure you have at least three points above, below, and including the resonant frequency. Note IRMS and VRMS are the values leaving the AC Voltage. Refer to your lecture notes on how to calculate average power.

R=10 [Ω]

 f [Hz] ω [rad/s] Z [Ω] IRMS [A] VRMS [V] PAVE [W]
1. Using Microsoft Excel or Google Sheets make a graph of the average power (y-axis) versus ω (x-axis). Make sure the graph has axes labeled with units included. Save a copy of the graph and include it in your submission.
2. Repeat #1-2 now with R=100 Ω and the circuit otherwise unchanged. Save a copy of the graph and include it in your submission.

R=100 [Ω]

 f [Hz] ω [rad/s] Z [Ω] IRMS [A] VRMS [V] PAVE [W]
1. Compare the two graphs qualitatively. What role does the resistance play in an RLC circuit?
2. Screen grab your circuit and include the picture in your lab report. Save the circuit for your own records.

Last Updated on June 18, 2020

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