In this simulation of an RLC circuit, you can adjust the frequency, resistance, capacitance, and inductance and see how these affect the current in the circuit. The top graph shows the voltage from the AC source and the current in the circuit, while the bottom graph shows the voltage across each component. There is also a vector diagram to the right showing how the impedance of the circuit is determined.

Here are some things to think about as you use the simulation to help understand an RLC circuit:

1.

As you adjust the settings of R, L, C, and the frequency, note how that affects the vector diagram that shows the total impedance of the circuit. The impedance is the effective resistance of the circuit – this is found by adding, as vectors, the effective resistances of the resistor, inductor, and capacitor.

2.

Set the parameters to give a positive phase angle, so the voltage leads the current. (The voltage peaks before the current – you should be able to see this on the graph.) You can decrease the phase angle by adjusting any of the four adjustable parameters. For each parameter, should you increase or decrease it to decrease the phase angle?

3.

Resonance occurs in the circuit when the current is in phase with the voltage. This is used in tuning some AM/FM radios. To understand how this works, use the following settings: f =60 Hz, R = 3 ohms, C = 300 µF, and L = 24 mH. If you change the frequency, note how the current is reduced – this gives you some idea of how the radio selectively amplifies a station at one particular frequency. To tune the radio to a different station, you can adjust, for instance, the value of C, which changes the resonance frequency. To see this in the simulation, re-set the capacitance to C = 150 µF. Note how this reduces the current at f = 60 Hz. For which frequency is the current maximized now?