WHAT IS ELECTRICITY?

For thousands of years, the nature of electricity puzzled and mystified some of the most brilliant minds. It wasn’t until scientists such as Benjamin Franklin, André-Marie Ampère, Alessandro Volta, and Michael Faraday contributed to our understanding of electricity that we began to unlock its secrets.

Step by step, bit by bit, we built a plausible model of electricity that fits a mathematical model and provides a real-world explanation of this phenomenon. Even after we had a basic understanding of the key relationships and the fundamentals of electricity, early pioneers such as Joseph Swan, Thomas Edison, Nikola Tesla, and George Westinghouse still struggled to harness its power for daily use in a safe and efficient manner.

During that time — the late 1800s and early 1900s — one of the first practical uses of electricity was to illuminate common areas such as city streets and town squares. New York City quickly became entangled — quite literally — in electrical wires and electricity. Horrified bystanders witnessed the accidental electrocution of several workers in the naked light of day, and electricity gained a reputation for being both mysterious and dangerous.

Thomas Edison used the public’s fear to protect his economic interests by promoting DC power distribution over AC power distribution, while George Westinghouse grew his business on the strength of AC and its inherent advantages over DC. The ensuing controversy did nothing to ease the public’s apprehension about electricity, nor did it help to clarify its nature or promote its understanding.

To this day, many people have little understanding of the nature of electricity. Some of us still have difficulty answering the question, “What is electricity?” After all, we can’t see it, hear it, or smell it. And we certainly don’t want to taste it or feel it.

An electrician might understand how to hook up a power distribution system but may not fully understand exactly how electricity behaves. By studying the fundamentals of electricity we can better understand how to use electricity safely, effectively, and legally, and we can excel at our jobs in the entertainment industry.

Electrons in Motion
The short answer to the question “What is electricity?” is the transfer of energy through the motion of charge-carrying electrons. Lightning is an example of electricity and of electrons — lots and lots of them — in motion.

Electricians are generally concerned with a much more controlled situation where electricity flows through a given path in a safe, predictable manner, but the electricity we use in shows is no different than that in a lightning strike, a static discharge, or a flashlight battery. Each is an example of the transfer of energy through the motion of electrons.

But from where do these electrons come? The answer can be found in one of the most basic building blocks of the universe, the atom.

The Atom
The word “atom” comes from the Greek word atomos, meaning indivisible. It is the smallest particle that still retains the properties of the element from which it comes. If you took your side cutters and cut a small strand of copper from a cable, you would have billions of copper atoms. If you then cut that piece in half, and then in half again, and over and over until you got down to the single piece that still looked and acted like copper, then you would have an atom.

But you would have to be pretty good with those cutters. One atom of copper is approximately 10–12 meters in diameter. Put another way, it takes about 254 billion copper atoms placed side by side to make 1 inch. Good luck with that.

Atoms are literally everywhere. They make up the air you breathe, the water you drink, the clothes you wear, and the food you eat. They are the building blocks of the universe.

Subatomic Particles
Despite what the early Greeks thought, atoms can be divided. It turns out that they are made up of even smaller subatomic particles called electrons, neutrons, and protons. These subatomic particles are very important to the understanding of electricity. Electrons carry a negative charge, protons have a positive charge, and neutrons have no charge at all.

It’s the interaction of these charges that causes the phenomenon we call electricity. An atom has a nucleus that is made up of a number of protons and neutrons bound by nuclear forces. The nucleus is surrounded by an electron cloud made up of electrons in orbit about the nucleus. The specific number of neutrons, protons, and electrons depends on the element. For example, copper atoms normally have 29 protons, 35 neutrons, and 29 electrons.

Electrostatic Charges
The vast majority of atoms are electrically neutral because the number of negatively charged electrons is balanced by the number of positively charged protons, creating a net charge of zero. In a copper atom, for example, the number of positively charged protons, 29, matches the number of negatively charged electrons; thus the charges cancel each other, resulting in a net charge of zero.

It’s important to understand the electrostatic attraction between charges: opposite charges attract and like charges repel. For example, two protons will repel each other and two electrons will repel each other, but a proton will attract an electron.

The force of attraction or repulsion depends on two factors: the magnitude of the individual charges and the proximity of the charges. The magnitude of the individual charges, whether they are attracting or repelling, directly affects how strongly the force of attraction or repulsion will be.

Since a single proton carries a fixed positive charge and a single electron carries a fixed negative charge, the magnitude of an individual charge depends on the number of protons or electrons involved.

An atom with two protons, for example, will have twice the force of attraction to an electron as will an atom with a single proton. The force of attraction also varies exponentially as the inverse of the distance between the charges. If the distance between the two charges is doubled, then the force of attraction or repulsion will decrease by a factor of four; if the distance is halved, then the force will increase by a factor of four.

Force = k(q1⋅q2 )÷ d^2,

where force is the magnitude or strength of the force exerted, k is a constant, q1 and q2 are charges on the particles, and d is the distance between them.

This relationship shows how the force of attraction or repulsion depends on the magnitude of the two charges, q1 and q2, and the distance of separation. This law of attraction or repulsion of electrostatic charges is called Coulomb’s law after Charles-Augustin de Coulomb, a French physicist who discovered the relationship.

Since opposite charges attract and like charges repel, the electrons in an electron cloud are held in orbit about the nucleus of an atom by their electrostatic attraction to the protons. However, some of the electrons are orbiting so far away from the nucleus that the bond is relatively weak.

To give you an idea of the relative distances involved, suppose we could scale our copper atom so that the nucleus was the size of a golf ball. Then you would have to go about 2.41 kilometers (a mile and a half) before you would find the outermost electrons.

If another external force, like a voltage, is applied, the electrons in the outer orbit can sometimes be pulled away from their associated atom. When that happens, the atom becomes “ionized.” The free electrons that are pulled away from the nucleus of an atom can either “drift” toward the force of attraction — from the applied voltage — or they can reassociate with another atom by “falling” into its orbit.

An ionized atom that is missing one or more electrons is known as a “hole” in electronics parlance, and it carries a net positive charge. Every electron carries the same quantity of charge. The coulomb (C) is the standard unit of electric charge as defined by the International System of Units (abbreviated SI for the French Système International d’Unitès).

It is derived from the amount of charge carried by 1 ampere of current in 1 second. It turns out that a single electron carries a charge of –1.6022 × 10−19 coulombs (–0.00000000000000000016022 C). Put another way, it takes 6.241506 × 10^18 electrons (6,241,506,000,000,000,000 electrons) to make 1 coulomb of charge.

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