This simulation is an introduction to AC (alternating current) circuits, allowing you to connect a resistor, a capacitor, or an inductor to an AC source. Resistors work much as they do in DC, with Ohm’s Law still applying. When a capacitor or an inductor is used instead of the resistor, the situation is a little more complicated.

The first step in figuring out what happens in an AC circuit is to simply observe what happens to the current as you make changes in the circuit. Here are some things to try:

1. | Note the phase relationship between the voltage and current. Are they always in phase?

2. | Adjust the frequency. Does the magnitude of the current change? How?

3. | Adjust the value of R, C, or L, depending on what you have connected. Does a decrease in these values always result in an increase in the current?

4. | With a capacitor in the circuit, adjust the frequency and the capacitance. How can you maximize the current in the circuit? How can you minimize it?

5. | With an inductor in the circuit, adjust the frequency and the inductance. How can you maximize the current in the circuit? How can you minimize it?

One thing you can use to help you understand the circuit is to remember that Kirchoff’s loop rule still applies. Because there is only one device connected to the AC source, the potential difference across the device must equal the instantaneous value of the voltage from the source. The basic question is, how is a potential difference created across a particular device? Resistors are straightforward; the larger the current through a resistor, the larger the potential difference across it. This explains why the voltage and current are in phase for resistors.

With the capacitor connected in the circuit, observe the animation of the capacitor charging and discharging to help answer the following questions. How is a potential difference created across a capacitor? To change the potential difference quickly, does this require a large current or a small current? Does this help explain the observed relationship between the current and voltage? Do you agree with the statement that for a capacitor, the current in the circuit is proportional to the rate of change of voltage? What are the implications of this? For instance, what happens to the current if the frequency is increased?

With the inductor in the circuit, use the animation showing the magnetic field created by the inductor to answer these questions. How is a potential difference created across an inductor? (Hint - does it have anything to do with a changing magnetic flux?) To create a large positive potential difference, the current must change - how? Do you agree with the statement that for an inductor, the voltage is proportional to the rate of change of current? What are the implications of this?