If you have spent some time around electrical devices, you are probably aware of the fact that there are multiple ways to transmit electricity over circuits. The two methods of electrical current transfer we use in most systems, are alternating current (AC), and direct current (DC). In case you are curious, ill give a brief explanation of what the different types of electric current are, and why we use them. We should be able to answer many common questions, such as what the different systems mean, why most electrical device charges have those boxes in the middle of the cord, and why we use the different methods of allowing electrical energy to flow.
One of the best analogies for electrical flow is a pipe with water inside of it. In this analogy, the pipes in your house (analogous to outlets) would be pressurized. If you plug in an appliance, the two prongs of the plug allow water to flow in one prong, and out the other. Inside of your appliance, the flow of water will be converted to whichever type of energy you need to run the appliance. If you are ever confused by the descriptions of electrical energy in this chapter, imagine the electrons as water inside of a pipe. The pipe represents the wire, and allows electrons to flow through it.
In a DC system, you could think of it as water flowing smoothly and constantly, coming in one prong, and out the other. The water simply enters on one side, flows through the system, and flows out the other side. This is perfectly analogous to how electricity flows through a wire. The electrons are everywhere in the wire, and once they begin to move (pushing each other) their energy can be used to do work. In this system, you need to have electrons flowing in on one side, and out on the other. These are your positive and negative terminals, where the circuit is completed. This also might be a good way to help people understand how you need to complete a circuit for electricity to flow. If the electricity has nowhere to go, it wont flow through a circuit. If you graphed the flow of electricity in a DC system, it would be a smooth line, with very little variability in the power being supplied.
DC power is commonly used in a variety of small electrical devices. Any time you have a device with a circuit board, you will need steady, unidirectional flow of electrons. The circuits are designed to function when energy is fed through them in this manner. This is why most electronic devices have a small adaptor built into their chargers. Your computer has a built in adaptor, converting AC into DC while you work. Household power is AC, and these devices require DC.
AC systems use a rapidly oscillating flow of electrons. In America, the most common AC frequency is 60 hz, which means that the electricity changes directions 60 times every second. This motion is more akin to waves on a beach, where surges of energy come in, and then flow back out. This energy can also be captured by household appliances, and used to perform useful functions. The rapid back and forth oscillations can be used to power functions. If you graphed the power in an AC system, it would form a smooth sine wave, alternating predictable between two extremes.
AC is very useful for long distance transmission of power. Because of the way electricity functions, when it is transmitted long distances using DC, there is a lot of power lost during transmissions. The electrons bump into each other, and cause a lot of overall energy loss. However, if you use AC, you can drastically reduce the amount of energy which is lost during long distance transmission. This is why the electrical grid uses an alternating current system to transfer power. Typically, power will be generated in a direct current circuit, changed to alternating current for transmission, and then is frequently changed back to DC for use, depending on what device you are plugging in.
However, the frequency at which an alternating current system oscillates is not set in stone. In the USA, 60hz is used, because the companies who initially developed the grid began using 60hz equipment, and it quickly became convenient and cheap to continue with the already established protocols However, many other countries use 50 hz, and their power grids work just fine. However, this could be a problem if you are using adaptors made for one electrical grid in a different region. If you are going on vacation, make sure that your electrical devices will all be able to interface with the power grid without causing themselves or you any harm.