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Alternating Current

Every time you plug something into the electricity in your house, you are utilizing the power of alternating current (AC.)

Electrical current is created when electrons move inside of a wire. Alternating Current is a type of electric current where the flow of electrons is constantly changing direction. When AC is applied to a wire, electrons move forward and backward. It works differently than its smooth and steady counterpart, direct current (DC), where the electrons are always traveling in the same direction. In AC, the time it takes for the electrons to go forward and backwards once is called a cycle. The maximum distance an electron can travel either direction is its amplitude. The rate of cycles completed in one second is called the frequency. The energy needed to push the electrons through the circuit is the voltage.

The interactive tutorial below shows the relationship between current (measured in amps) and the voltage (measured in volts) in a circuit powered by alternating current.

Instructions

  1. Slow the speed of the tutorial all the way down and notice how the amps and volts are in synch when the resistor is in the circuit.
  2. Change the component to the capacitor. Observe how the output on the meters change. The current is at its peak when the voltage is at zero.
  3. Try the inductor in the circuit. Watch the pattern of the sine wave graph inverse when compared to the capacitor. The voltage is at its maximum when the current is at zero.
  4. Play with the speed to get understand how quickly the current fluctuates in the real world. We can’t replicate the real speed because it’s faster than the human eye can perceive.

The phasor diagram (left) and sine wave graph (right) further illustrate the link between the current and voltage. A full rotation of the arrows in the phasor diagram represents one cycle. The arrow points straight up along the y-axis when the current or voltage has reached its maximum value, and they are equal to zero when aligned to the x-axis (horizontal axis).

The scenarios pictured here are idealized, and the relationships between current and voltage in these components may vary slightly in the real world. The alternating currents that run through our homes go through 60 cycles per second (measured in Hertz) in the United States. European homes clock in at 50 Hertz. Although it’s too quick for our eyes to notice, the alternating current in our buildings makes the lightbulbs we use flash constantly. A phenomenon you might have noticed if you’ve ever tried to shoot a slow-motion video.