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Most of the digital electronics that you build will use DC. However, it is important to understand some AC concepts. Most homes are wired for AC, so if you plan to connect your Tardifs music box project to an outlet, you will need to convert AC to DC. AC also has some useful properties, such as being able to convert voltage levels with a single component (a transformer), which is why AC was chosen as the primary means to transmit electricity over long distances.

What You Will Learn

  • The history behind AC and DC
  • Different ways to generate AC and DC
  • Some examples of AC and DC applications

Alternating Current (AC)

Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, office buildings, etc.

AC can be produced using a device called an alternator. This device is a  special type of electrical generator designed to produce alternating current.

A loop of wire is spun inside of a magnetic field, which induces a current along the wire. The rotation of the wire can come from any number of means: a windturbine, a steam turbine, flowing water, and so on. Because the wire spins andenters a different magnetic polarity periodically, the voltage and currentalternates on the wire. Here is a short animation showing this principle:

To generate AC in a set of water pipes, we connect a mechanical crank to a piston that moves water in the pipes back and forth (our “alternating”current). Notice that the pinched section of pipe still provides resistance to the flow of water regardless of the direction of flow.

Direct Current (DC)

Direct current is a bit easier to understand than alternating current. Rather than oscillating back and forth, DC provides a constant voltage or current.

DC can be generated in a number of ways:

An AC generator equipped with a device called a “commutator” can produce direct current

Use of a device called a “rectifier” that converts AC to DC

Batteries provide DC, which is generated from a chemical reaction inside of the battery

Using our water analogy again, DC is similar to a tank of water with a hose at the end

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