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.
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 -- a ubiquitous form of energy resulting from the motion of charged particles, like electrons. 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 travel to Greece, where inquisitive ancients puzzled over the same phenomena that zaps you when you touch a metal object after shuffling over the carpet on a cold, dry day.
Electrostatics and Coulomb's Law
Even though they didn't fully understand it, ancient people knew about electricity. Thales of Miletus, a Greek philosopher known as one of the legendary Seven Wise Men, may have been the first human to study electricity, circa 600 B.C. By rubbing amber -- fossilized tree resin -- with fur, he was able to attract dust, feathers and other lightweight objects. These were the first experiments with electrostatics, the study of stationary electric charges or static electricity. In fact, the word electricity comes from the Greek elektron, which means amber.
The experiments wouldn't continue until the 17th century. That's when William Gilbert, an English physician and amateur scientist, began to study magnetism and static electricity. He repeated the research of Thales of Miletus, rubbing objects together and charging them by friction. When one object attracted or repelled the other, he coined the term "electric" to describe the forces at work. He said these forces developed because the rubbing action removed a fluid, or "humour," from one of the objects, leaving an "effluvium," or atmosphere, around it.
This concept -- that electricity existed as a fluid -- persisted into the 1700s. In 1729, English scientist Stephen Gray observed that certain materials, such as silk, didn't conduct electricity. His explanation was that the mysterious fluid described by Gilbert could travel through objects or be hampered from traveling. Scientists even built jars to hold this fluid and study its effects. The Dutch instrument makers Ewald von Kleist and Pieter van Musschenbroek created what is now known as a Leyden jar, a glass jar containing water and a nail that could store an electrical charge. The first time Musschenbroek used the jar, he received a massive shock.
By the later 1700s, the scientific community was beginning to get a clearer picture of how electricity worked. Benjamin Franklin ran his famous kite experiment in 1752, proving that lightning was electrical in nature. He also presented the idea that electricity had positive and negative elements and that the flow was from positive to negative. Approximately 30 years later, a French scientist by the name of Charles Augustin de Coulomb conducted several experiments to determine the variables affecting an electrical force. His work resulted in Coulomb's law, which states that like charges repel and opposite charges attract, with a force proportional to the product of the charges and inversely proportional to the square of the distance between them.
Coulomb's law made it possible to calculate the electrostatic force between any two charged objects, but it didn't reveal the fundamental nature of those charges. What was the source of the positive and negative charges? As we'll see in the next section, scientists were able to answer that question in the 1800s.
Electricity and Atomic Structure
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 the modern era of 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 these atoms are so reluctant to share electrons, these materials can't conduct electricity very well, if at all. These materials are electrical insulators.
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.
Some of us at HowStuffWorks.com like to think of atoms as pet dogs and electrons as a case of fleas. Dogs that lived inside or within a fenced-in area, thereby keeping those pesky fleas contained, would be the equivalent of an electrical insulator. Free-roaming mutts, however, would be electrical conductors. If you had one neighborhood of indoor, pampered pugs and one neighborhood of unfenced basset hounds running wild, which group do you think could spread an outbreak of fleas the fastest?
So, 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.
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.
Thanks to Wooly Willy, we can see that there's 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.
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.
Generators form the heart of a modern power station. In the next section, we'll take a look at how one of these stations works.
In Michael Faraday's generator, coils of copper wire rotating between the poles of a magnet produce a steady current of electricity. One way to rotate the disk is to crank it by hand, but this isn't a practical way to make electricity. Another option is to attach the shaft of the generator to a turbine and then let some other energy source power the turbine. Falling water is one such energy source, and, in fact, the first major plant ever built took advantage of the enormous kinetic energy delivered by Niagara Falls.
George Westinghouse opened that plant in 1895, but the principles of its operation haven't changed much since then. First, engineers build a dam across a river to create a reservoir of stored water. They place a water intake near the bottom of the dam wall, which allows water to flow from the reservoir and through a narrow channel called a penstock. The turbine -- imagine a huge propeller -- sits at the end of the penstock. The shaft from the turbine goes up into the generator. When the water moves across the turbine, it spins, rotating the shaft and, in turn, rotating the copper coils of the generator. As the copper coils spin within the magnets, electricity is produced. Power lines connected to the generator carry electricity from the power plant to homes and businesses. Westinghouse's Niagara Falls plant was able to transport electricity more than 200 miles (322 kilometers).
Not all power plants rely on falling water. Many take advantage of steam, which acts like a fluid and can therefore transfer energy to a turbine and, ultimately, to a generator. The most popular way to make steam is to heat water by burning coal. It's also possible to use controlled nuclear reactions to turn water into steam. You can read about the various types of power stations in How Hydropower Plants Work, How Wind Power Works and How Nuclear Power Works. Just keep in mind that they all work on the same basic principle of converting mechanical energy -- spinning turbine -- into electrical energy.
Of course, using a generator to make electricity is just the beginning. After you get your electrons moving along, you'll need an electrical circuit to do anything with it. Find out why next.
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.
- 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 light bulb 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 light bulb, 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. Because motors are so important to everyday activities and because they are, in essence, a generator working in reverse, we'll examine them more closely in the next section.
As we've already discussed, a generator converts mechanical energy into electricity. A motor works on the same principles, but in the opposite direction -- it converts electrical energy into mechanical energy. To do this, a motor needs a special kind of magnet known as an electromagnet. In its simplest form, this consists of an iron bar wrapped in a coil of wire. If you pass an electric current through the wire, a magnetic field is formed in the iron bar, and it becomes a magnet, with definite north and south poles. Turn off the current, and the magnetic properties disappear.
By themselves, electromagnets are useful things. You can use them to pick up metal objects, carry the objects somewhere and then drop them by just turning off the power. For example, roofers use them to pick up nails that have fallen by accident into a homeowner's yard. And wrecking yards have cranes with built-in electromagnets strong enough to pick up and move entire cars.
Electromagnets are especially useful when they're placed on an axis between two stationary magnets. If the electromagnet's south pole is situated against the south pole of one stationary magnet and its north pole against the north pole of the other stationary magnet, the electromagnet will rotate until opposite poles line up. This wouldn't be very helpful, except the polarity of electromagnets depends on the direction of current flow. Pass electric current in one direction, and the magnet's north pole will be on one side; reverse the current flow, and the north pole will be on the opposite side. In motors, a device known as a commutator reverses the direction of flow of electric current. As the poles of the electromagnet flip back and forth, the magnet is able to rotate without interruption. This is a brief explanation of course, so you may want to read How Electric Motors Work for all of the details.
As it turns out, the mechanical energy created in an electric motor can be put to good use in a variety of machines. Many tools in your garage, appliances in your house and toys kids play with rely on motors. Some of these motors require a large current to operate. Others, such as small DC motors used in robots and models, need very little voltage or current to perform efficiently. We'll continue our conversation about voltage and current in the next section.
Voltage, Current and Resistance
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 typically measure in watt-hours or kilowatt-hours. 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 wattage. 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 light bulb.
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 called Ohm's law 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 (measured in amps), V is voltage (measured in volts) and R symbolizes resistance (measured in ohms).
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 light bulb, you can see this water analogy in action. The filament of a light bulb 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 light bulb 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.
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 Versus Alternating Current
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.
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.
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.
- How Atoms Work
- How Batteries Work
- How Circuit Breakers Work
- How Electric Motors Work
- How Emergency Power Systems Work
- How Light Bulbs Work
- How Lightning Works
- How Power Grids Work
- How Living Off the Grid Works
- How Magnets Work
- Is it possible to generate electricity directly from heat?
- Why is it that some appliance plugs have three prongs and others have only two?
- Are fluorescent bulbs really more efficient than normal light bulbs?
More Great Links
- "Electricity." Britannica Encyclopædia. 2008. (Dec. 17, 2008) http://www.britannica.com/EBchecked/topic/182915/electricity
- Gundersen, P. Erik. The Handy Physics Answer Book. Visible Ink Press. 2003.
- "Michael Faraday." Britannica Online Encyclopædia. 2008. (Dec. 17, 2008) http://www.britannica.com/EBchecked/topic/201705/Michael-Faraday
- Rasenberger, Jim. "Urban tactics; Fade to Black." New York Times. Jan. 2, 2005. (Dec. 17, 2008) http://query.nytimes.com/gst/fullpage.html?res=9804EEDC1439F931A35 752C0A9639C8B63&sec=&spon=&pagewanted=1
- Ruddick, Nicholas. "Life and Death by Electricity in 1890: The Transfiguration of William Kemmler." Journal of American Culture. Winter 1998.
- Wilson, Tracy V. "How Magnets Work." HowStuffWorks.com. April 2, 2007. (Dec. 17, 2008) http://science.howstuffworks.com/magnet.htm
- Wright, Michael and Mukul Patel, ed. How Things Work Today. Crown Publishers. 2000.