What’s AC?

Ever had an issue with your car’s alternator? It’s not just a car thing; most appliances (especially those that uses motors like blenders and hair dryers) use alternating current as opposed to direct current. But what’s the difference and what’s the point? This article will explain that:


An alternating current describes a flow of charge that changes direction repeatedly. When the current reverses, so does the voltage level. Alternating Current is used to bring power to houses, office buildings, schools, and just about any major structure on the grid.

So how is it done? Like I said before, alternating current is created by using a device called the alternator. The alternator is an electrical generator made specifically for creating alternating current.

They function like this: a loop of wire is spun inside of a magnetic field, which then induces an electric current along a wire. The rotation of the wire can come from all kinds of sources, from a wind turbine, a steam turbine, flowing water, etc. Because the wire spins, its rotation causes it to enter a different magnetic polarity periodically. That means that the voltage and current on the wire is going to alternate too.


Water pipes can also be used to this end; simply attaching a mechanical crank to a piston that moves water in a pipe back and forth will cause it to run in both directions.

If you use an oscilloscope to measure the voltage of a circuit with AC, you’re going to see a bunch of different waveforms. The most common of these is the sine wave; the AC in most homes and buildings use a current that has an oscillating voltage that can be charted as a sine wave.

Square waves can occur too, but generally they only happen in digital contexts in which the operation of electronics is being tested. You can even find triangle wave readings if you’re checking out an amplifier or other instrument used for sound synthesis.

So why use alternating current instead of direct current, and why are almost all homes powered from the grid on the AC circuit? Generating and transporting alternating current across long distances is much easier than transporting direct current. Alternating currents lose less energy when they hit high voltage numbers (over 110kV) because those high voltages then translate into lower currents, which translate into less heat generated in the power line due to resistance. Since that heat is just a waste of energy, it’s a more efficient use of natural and financial resources to avoid it as much as possible.

AC can also be converted to and from high voltages easily using transformers, a luxury that direct currents do not allow for. AC is capable of powering electric motors (motors convert electrical energy into mechanical energy). Motors need alternating currents in order to spin the electromagnet (or actual magnet in the case of brushless motors) that create mechanical energy. Direct current would not have this effect, rendering motors impossible. That’s why we love AC!

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