Simple AC Circuits

This simulation shows a simple circuit consisting of an alternating voltage source and, depending on the selection, a resistor (without inductance), a capacitor, or an ideal coil (without resistance). In addition there are meters for the voltage ( U ) and the current ( I ).

The "Reset" button brings the circuit to its initial state. You can start or stop and continue the simulation with the other two buttons. If you choose the option "Slow Motion", the movement will be five times slower.

It is possible to vary the values of frequency, maximum voltage, resistance, capacitance, or inductance. After pressing the "Enter" key the program will indicate the new value of the maximum current.

This applet requires a Java enabled web browser.

Below the circuit on the left is a phasor diagram. This makes it possible to see the momentary oscillation phases from the position of the two pointers (voltage, current ).   When the vector points to the right we have the maximum value, vertical is the zero value and left is the negative maximum.  The projection of a pointer onto the horizontal axis corresponds to the momentary value of U respectively I.

On the bottom right there is the graph of voltage and current with respect to time.
Notice when the resistor is in the circuit, the current and the voltage are in phase.  This means that when the voltage is at a peak, the current is too.  When the voltage is zero, the current is too.  Notice in the phasor diagram the current and voltage vectors line up.  We could say they are 0 out of phase.
Notice when the capacitor is in the circuit, the current leads the voltage by 90.  This means that when the current is a maximum the voltage is zero.
When the coil or inductor is in the circuit, the current lags behind the voltage by 90.  This also means that when the voltage is a maximum the current is zero.

URL: http://home.a-city.de/walter.fendt/physengl/accircuit.htm
Walter Fendt, June 13, 1998
Last modification: January 21, 1999

Slight modifications of the description were made by Steve Wirt.

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