How Electricity Works

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Introduction to How Electricity Works

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Humans have an intimate relationship with electricity, to the point that it's virtually impossible to separate your life from it. Sure, you can flee from the world of crisscrossing power lines and live your life completely off the grid, but even at the loneliest corners of the world, electricity exists. If it's not lighting up the storm clouds overhead or crackling in a static spark at your fingertips, then it's moving through the human nervous system, animating the brain's will in every flourish, breath and unthinking heartbeat.

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When the same mysterious force energizes a loved one's touch, a stroke of lightning and a George Foreman Grill, a curious duality ensues: We take electricity for granted one second and gawk at its power the next. More than two and a half centuries have passed since Benjamin Franklin and others proved lightning was a form of electricity, but it's still hard not to flinch when a particularly violent flash lights up the horizon. On the other hand, no one ever waxes poetic over a cell phone charger.

Electricity powers our world and our bodies. Harnessing its energy is both the domain of imagined sorcery and humdrum, everyday life -- from Emperor Palpatine toasting Luke Skywalker, to the simple act of ejecting the "Star Wars" disc from your PC. Despite our familiarity with its effects, many people fail to understand exactly what electricity is. When put to the question, even acclaimed inventor Thomas Edison merely defined it as "a mode of motion" and a "system of vibrations."

In this article, we'll try to provide a less slippery answer. We'll illuminate just what electricity is, where it comes from and how humans bend it to their will.

For our first stop, we'll start small -- very small. The roots of electricity take place inside the atom itself.

Electricity Basics

Simplest model of an atom

Toward the end of the 19th century, science was barreling along at an impressive pace. Automobiles and aircraft were on the verge of changing the way the world moved, and electric power was steadily making its way into more and more homes. Yet even scientists of the day still viewed electricity as something vaguely mystical. It wasn't until 1897 that scientists discovered the existence of electrons -- and this is where electricity starts.

Matter, as you probably know, is composed of atoms. Break something down to small enough pieces and you wind up with a nucleus orbited by one or more electrons, each with a negative charge. In many materials, the electrons are tightly bound to the atoms. Wood, glass, plastic, ceramic, air, cotton -- these are all examples of materials in which electrons stick with their atoms. Because the electrons don't move, these materials can't conduct electricity very well, if at all. These materials are electrical insulators.

Holy Electricity

In the late 19th century, electricity truly had a noble or even divine reputation -- to the extent that members of the scientific community protested the idea of the electric chair as a degradation of both electricity and the scientific breakthroughs that made electrocuting a criminal possible. What might these critics have thought of such modern marvels as the battery-powered blackhead remover or the dance-floor horror known as the electric slide?

Most metals, however, have electrons that can detach from their atoms and zip around. These are called free electrons. The loose electrons make it easy for electricity to flow through these materials, so they're known as electrical conductors. They conduct electricity. The moving electrons transmit electrical energy from one point to another.

Think of electrons as pet dogs and a negative charge as a case of fleas. Homes where the dogs lived inside or within a fenced-in area would be the equivalent of an electrical insulator. Homes where the pets roamed free, however, would be electrical conductors. If you had one neighborhood of indoor, pampered pugs and one neighborhood of unfenced, free-roaming basset hounds, which group do you think could spread an outbreak of fleas the fastest?

Dogs aside, electricity needs a conductor in order to move. There also has to be something to make the electricity flow from one point to another through the conductor. One way to get electricity flowing is to use a generator.

Generators

If you've ever moved paper clips around with a magnet or killed time arranging metal shavings into a beard on a "Wooly Willy" toy, then you've dabbled in the basic principles behind even the most complicated electric generators. The magnetic field responsible for lining up all those little bits of metal into a proper Mohawk haircut is due to the movement of electrons. Move a magnet toward a paper clip and you'll force the electrons in the clip to move. Similarly, if you allow electrons to move through a metal wire, a magnetic field will form around the wire.

There is a definite link between the phenomena of electricity and magnetism. A generator is simply a device that moves a magnet near a wire to create a steady flow of electrons. The action that forces this movement varies greatly, ranging from hand cranks and steam engines to nuclear fission, but the principle remains the same.

Faraday: Patron Saint of Electricity

Nineteenth-century British physicist and chemist Michael Faraday paved the way for our modern electricity-driven world. The famed inventor created the first electric generator, called the dynamo, as well as the first electric motor. To learn more about the technology involved, read How Electric Motors Work and How Electromagnets Work.

One simple way to think about a generator is to imagine it acting like a pump pushing water through a pipe. Only instead of pushing water, a generator uses a magnet to push electrons along. This is a slight oversimplification, but it paints a helpful picture of the properties at work in a generator. A water pump moves a certain number of water molecules and applies a certain amount of pressure to them. In the same way, the magnet in a generator pushes a certain number of electrons along and applies a certain amount of "pressure" to the electrons.

In an electrical circuit, the number of electrons in motion is called the amperage or current, and it's measured in amps. The "pressure" pushing the electrons along is called the voltage and is measured in volts. For instance, a generator spinning at 1,000 rotations per minute might produce 1 amp at 6 volts. The 1 amp is the number of electrons moving (1 amp physically means that 6.24 x 10¹⁸ electrons move through a wire every second), and the voltage is the amount of pressure behind those electrons.

A generator may get your electrons moving along, but you'll need an electrical circuit to do anything with it. Find out why next.

Electrical Circuits

When you load a battery into an electronic device, you're not simply unleashing the electricity and sending it to do a task. Negatively charged electrons wish to travel to the positive portion of the battery -- and if they have to rev up your personal electric shaver along the way to get there, they'll do it. On a very simple level, it's much like water flowing down a stream and being forced to turn a water wheel to get from point A to point B.

Whether you are using a battery, a fuel cell or a solar cell to produce electricity, three things are always the same:

The source of electricity must have two terminals: a positive terminal and a negative terminal.
The source of electricity (whether it is a generator, battery or something else) will want to push electrons out of its negative terminal at a certain voltage. For example, one AA battery typically wants to push electrons out at 1.5 volts.
The electrons will need to flow from the negative terminal to the positive terminal through a copper wire or some other conductor. When there is a path that goes from the negative to the positive terminal, you have a circuit, and electrons can flow through the wire.

You can attach any type of load, such as a lightbulb or motor, in the middle of the circuit. The source of electricity will power the load, and the load will perform whatever task it's designed to carry out, from spinning a shaft to generating light.

Electrical circuits can get quite complex, but basically you always have the source of electricity (such as a battery), a load and two wires to carry electricity between the two. Electrons move from the source, through the load and back to the source.

Moving electrons have energy. As the electrons move from one point to another, they can do work. In an incandescent lightbulb, for example, the energy of the electrons is used to create heat, and the heat in turn creates light. In an electric motor, the energy in the electrons creates a magnetic field, and this field can interact with other magnets (through magnetic attraction and repulsion) to create motion. Each electrical appliance harnesses the energy of electrons in some way to create a useful side effect.

Voltage, Current and Resistance

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Resistance is one of the three basic units in electricity. The glowing filament in an incandescent lightbulb allows us to view resistance in action.

As mentioned earlier, the number of electrons in motion in a circuit is called the current, and it's measured in amps. The "pressure" pushing the electrons along is called the voltage and is measured in volts. If you live in the United States, the power outlets in the wall of your house or apartment deliver 120 volts each.

If you know the amps and volts involved, you can determine the amount of electricity consumed, which we measure in watts. Imagine that you plug a space heater into a wall outlet. You measure the amount of current flowing from the wall outlet to the heater, and it comes out to 10 amps. That means that it is a 1,200-watt heater. If you multiply the volts by the amps, you get the watts. In this case, 120 volts multiplied by 10 amps equals 1,200 watts. This holds true for any electrical appliance. If you plug in a light and it draws half an amp, it's a 60-watt lightbulb.

Let's say that you turn on the space heater and then look at the power meter outside. The meter's purpose is to measure the amount of electricity flowing into your house so that the power company can bill you for it. Let's assume -- we know it's unlikely -- that nothing else in the house is on, so the meter is measuring only the electricity used by the space heater.

Your space heater is using 1.2 kilowatts (1,200 watts). If you leave the space heater on for one hour, you will use 1.2 kilowatt-hours of power. If your power company charges you 10 cents per kilowatt-hour, then the power company will charge you 12 cents for every hour that you leave your space heater on.

Now let's add one more factor to current and voltage: resistance, which is measured in ohms. We can extend the water analogy to understand resistance, too. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate and the resistance is like the pipe size.

A basic electrical engineering equation spells out how the three terms relate. Current is equal to the voltage divided by the resistance. It's written like this:

I = V/r

where I stands for current, V is voltage and r symbolizes resistance.

Let's say you have a tank of pressurized water connected to a hose that you're using to water the garden. If you increase the pressure in the tank, more water comes out of the hose, right? The same is true of an electrical system: Increasing the voltage will result in greater current flow.

Now say you increase the diameter of the hose and all of the tank's fittings. This adjustment would also make more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow.

When you look at a normal incandescent lightbulb, you can see this water analogy in action. The filament of a lightbulb is an extremely thin wire. This thin wire resists the flow of electrons. You can calculate the resistance of the wire with the resistance equation.

Let's say you have a 120-watt lightbulb plugged into a wall socket. The voltage is 120 volts, and a 120-watt bulb has 1 amp flowing through it. You can calculate the resistance of the filament by rearranging the equation:

r = V/I.

So the resistance is 120 ohms. If it is a 60-watt bulb, the resistance is 240 ohms.

Beyond these core electrical concepts, there is a practical distinction between the two varieties of current. Some current is direct, and some current is alternating -- and this is a very important distinction.

Direct Current vs. Alternating Current

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This transformer helps transfer power traveling to and from California.

Batteries, fuel cells and solar cells all produce something called direct current (DC). The positive and negative terminals of a battery are always, respectively, positive and negative. Current always flows in the same direction between those two terminals.

The power that comes from a power plant, on the other hand, is called alternating current (AC). The direction of the current reverses, or alternates, 60 times per second (in the U.S.) or 50 times per second (in Europe, for example). The power that is available at a wall socket in the United States is 120-volt, 60-cycle AC power.

The big advantage that alternating current provides for the power grid is the fact that it is relatively easy to change the voltage of the power, using a device called a transformer. Power companies save a great deal of money this way, using very high voltages to transmit power over long distances.

How does this work? Well, let's say that you have a power plant that can produce 1 million watts of power. One way to transmit that power would be to send 1 million amps at 1 volt. Another way to transmit it would be to send 1 amp at 1 million volts. Sending 1 amp requires only a thin wire, and not much of the power is lost to heat during transmission. Sending 1 million amps would require a huge wire.

Tesla, Topsy and Edison

A bitter rivalry between electricity-savvy inventors may sound fictional, but the tension between Thomas Edison and Nikola Tesla was real. Tesla championed alternating current, while Edison insisted that it was too dangerous. The only casualties in this "war of currents" were the animals Edison publicly electrocuted with Tesla's high voltage system to prove his point. The early victims were dogs and cats, but Edison eventually electrocuted an elephant named Topsy [source: Ruddick].

So power companies convert alternating current to very high voltages for transmission (such as 1 million volts), then drop it back down to lower voltages for distribution (such as 1,000 volts), and finally down to 120 volts inside the house for safety. As you might imagine, it's a lot harder to kill someone with 120 volts than with 1 million volts (and most electrical deaths are prevented altogether today using GFCI outlets). To learn more, read How Power Grids Work.

There's one major electrical concept left that we haven't discussed: grounding.

Electrical Ground

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Power-distribution systems connect into the ground many times. Note the wire trailing down the side of the utility pole in this photo.

When the subject of electricity comes up, you will often hear about electrical grounding, or just ground. For example, an electrical generator will say, "Be sure to attach to an earth ground before using," or an appliance might warn, "Do not use without an appropriate ground."

It turns out that the power company uses the Earth as one of the wires in the power system. The planet is a good conductor, and it's huge, so it makes a handy return path for electrons. "Ground" in the power-distribution grid is literally the ground that's all around you when you are walking outside. It is the dirt, rocks, groundwater and so on.

If you look at a utility pole, you'll probably be able to spot a bare wire coming down the side of the pole. This connects the aerial ground wire directly to ground. Every utility pole on the planet has a bare wire like this. If you ever watch the power company install a new pole, you will see that the end of that bare wire is stapled in a coil to the base of the pole. That coil is in direct contact with the earth once the pole is installed, and is buried 6 to 10 feet (2 to 3 meters) underground. If you examine a pole carefully, you will see that the ground wire running between poles are attached to this direct connection to ground.

Similarly, near the power meter in your house or apartment there is a 6-foot (2-meter) long copper rod driven into the ground. The ground plugs and all the neutral plugs of every outlet in your house connect to this rod. Our article How Power Grids Work also talks about this.

Explore the links on the next page to learn even more about electricity and its role in technology and the natural world.

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