The Big List


1999 W. Beaty BSEE

What is electric charge? Well, there's an easy answer and a hard answer. Here is the easy answer:

Charge is...

...the stuff that flows during an electric current.
...the stuff that appears on a balloon when you rub it on your hair.
...the stuff that comes in two kinds: positive and negative.
...charge is like mass: it's a property, but it's also like "a stuff" ...a conserved quantity
...charge is the Plus/Minus electric poles (as opposed to North/South magnetic poles.)
...it's the stuff that causes electrical forces.
...charge is the "glue" that connects all of the e-field flux onto the protons and electrons.
...charge is the positive and negative stuff that forms atoms.
...charge is the stuff that is carried by electrons, protons, positrons, and other particles.
...charge is the medium through which electrical energy flows (like sound flows through air.)
...charge is the stuff that, when it wiggles fast, creates light.
...charge is the stuff that, when it wiggles slower, creates radio waves.
...charge is the stuff that, when it wiggles very slowly, creates energy in electric circuits.
...charge is the stuff that, when it flows or spins, creates magnetism.
...charge is the stuff that reflects light and makes objects visible.
...charge is the stuff that makes metals look metallic or "silvery."
...charge is the stuff that causes electrical attraction and holds everyday objects together.
...charge is the stuff inside of wires that is movable, almost fluid.
...charge is the stuff inside of nonconductors that is immobile and "frozen" in place.
...charge is the stuff that is measured in units called Coulombs.
...charge is the stuff that scientists once called "quantity of electricity" and "particles of electricity."


If we look up "electric charge" in a dictionary, we encounter a problem. The definition of "charge" is circular. What is charge? It's the stuff that causes electrical phenomena. What are electrical phenomena? Those are the things caused by charge! Simple, no?

There is a good reason why the definition of "charge" is circular. Like mass, length, and time, Electric Charge is a "fundamental." Many dictionaries say this: "Electric charge: a fundamental property of matter." The word "Charge" is used to define other things, and therefore the definition of the word "charge" becomes a serious problem! What is an electric current? It is a flow of charge. What is electric charge? It is the stuff that flows during an electric current! The circular definition is hard to avoid because normal definitions are based upon deeper concepts, and when we finally arrive at the deepest concepts of all, we cannot "take them apart" into their fundamental pieces. What is charge? What is mass? What is time? This is like asking "what is 'WHAT'?" or "what is 'IS'?" Very hard to answer. Yet there is a way to do it: look at the context in which we use the term. In other words we can work backwards and define Charge in terms of more complicated concepts. Yes, the definitions still will be circular. However, the definitions point at each other in a certain special pattern. We can understand "charge" by becoming familiar with this pattern.

To find the special pattern, go look at the list at the top of this page. THAT'S where the words "electric charge" are explained.

Electric charge is a component of atoms. In other words, after we have broken an object into molecules, and broken the molecules into atoms, when we break the atoms apart we discover particles of electric charge. Charge is material, it is like atoms but it is one step lower than atoms. Most science textbooks tell us that solid objects are made of atoms. It is also valid to state that solid objects are made of electric charge. Objects are made of equal quantities of positive and negative charge, and objects stay together because of the attraction between the quantities of opposite charge inside them. Chemical bonds are electrical in nature.

Charge flow

When charge moves, what do we call it? Well, if the positive and negative charges move along together, we call it "physical motion." Since matter is composed of charge-carrying particles, all physical motion is a motion of charge, but in most cases both the negative and the positive charges move along as one. On the other hand, whenever opposite charges move separately, that's when interesting things occur. Opposite charges moving along together are "mechanical", while opposite charges moving differently are "electrical." If the negative charge in an object should start moving while the object's positive charge stays at rest, then we call that motion a flow of electricity, or an electric current. The words "electric current" mean the same as "charge flow."

Charge: it's not energy

Charge is not energy. A fixed quantity of charge can possess many different amounts of energy at the same time (and note the same charge in different values of capacitor.) Also, if you know the amount of charge present, you have no knowledge of the amount of energy. Also, charge and energy move differently: in AC cables the charges sit in one spot and slowly wiggle, while the energy flows across the circuit at almost the speed of light. (Insight: charge is different from electrical energy in thesame way that air is different from sound waves.) Inside electric circuits, charge flows slowly in a circle like a drive belt, while energy moves quickly from the source to the load. Some people think that since charge and electrical energy are mysterious and invisible, they must be the same thing. But see below: electrical energy is invisible, but charge is definitely VISIBLE. And finally, J. C. Maxwell points out that charge and energy MUST be two different things, since the amount of energy is calculated by multiplying the amount of charge by the voltage of that charge.

If charge is not energy, then what exactly is it? Well, a block of iron can be lifted above the Earth in order to store potential energy, or it can be spun rapidly to store kinetic energy, but the mass of the iron is not the energy being stored. So there's our answer by analogy: "charge" is a concept very similar to "mass." We can store potential energy by forcibly separating the opposite charges in a capacitor, or we can store kinetic energy by forcing the charges in a copper inductor to spin around the spiral windings. But charge stays constant while doing this, and mass stays constant when lifting or spinning an iron disk. (Yes yes Einstein, but at this level of Classical physics, Relativity is still just a distraction. And, we don't have to double the weight of a flywheel in order to double the KE stored by its spinning motion!)

Charge: not just a property, but also "a stuff."

Charge is just a property, so how can a property move from place to place? Well, the same is true of mass. Mass is a property, but it also behaves like "a stuff" which can be moved around. Fortunately we have a term for properties which act like stuff. They're called "conserved quantities." Mass is a conserved quantity: in order to get rid of mass inside an enclosure, we can't just make it vanish, instead we must take that mass past the walls of the enclosure. Charge is like mass: a conserved quantity, "a stuff." This is very different than non-conserved properties. The color blue is a property of a painted object, but "blue" can easily vanish: just heat the object so the blue is burned to black! Mass and charge are different: we can't easily get rid of them, instead we must remove them. (In more rigorous language, a conserved quantity is one which, in order to change the amount inside a closed "Gaussian" surface, we must pass it through that surface.) So, charge is a "stuff-like" property. It's a mistake to think charge (or mass) is anything like the blue color of paint, or to say they're "just a property."

Charge is "poles"

When the positive and negative charges of matter are sorted out and pulled away from each other, "static electricity" is the result. When (+) is pulled away from (-), an invisible force field connects them and causes them to attract each other. This field is similar to magnetism in many ways, but it is not magnetism, it is called an Electrostatic Field, or "e-field." With magnetism, the lines of force spring from the north and south poles of magnets, and these lines seem to connect the opposite magnetic poles together. In Electrostatics, the electrical lines of force connect the (+) and (-) poles together. What is charge? It is the "pole" where the electrical lines of force come to an end. Follow the lines of a static "e-field" along, and eventually you'll arrive at a small bit of "charge." Electric charge is the glue which attaches the flux lines of e-field to the particles of matter.

Charge: it's not invisible

Charge is not invisible. Whenever light bounces off an object, it bounces off the outside of the atom, and the outside of an atom is made of negative charges. In other words, electric charge reflects light. Yet when we rub a balloon on our hair, the balloon (and the hair) don't look different. How can charge be visible if we see no visible difference when we electrify a balloon? Simple: the balloon's excess charge is way too small. The imbalanced charge caused by rubbing a balloon on your head is like a teacup poured into the ocean: it is very tiny when compared to the charge which is already there. The balloon is made of charge, and the amount of charge that is added or removed by the hair is incredibly small. If we could add a billion times more charge to that "charged up" balloon, then we would see some changes in its color. But the poor balloon would instantly explode violently outwards because alike charges on its surface would fiercely repel each other. (Here's a clue: when a significant portion of the positive charges in a block of Uranium become disconnected and fly away from each other, that's called a nuclear explosion.)

Here is a way to see charge directly: look at the surface of a wire. Metals look metallic because they contain a "fluid" composed of movable electrons. This electrical "fluid" is an excellent reflector of light waves, and it causes the surfaces of metals to act like mirrors. It's these same electrons which flow during an electric current. The "silvery" stuff of a metal is the charge. What is charge? It is a "silver liquid" which is found in all metals, and which can be forced to flow. Even though the charge is visible, its flow is not. Look carefully at wires in an operating electric circuit and you won't see anything moving along. This is not very mysterious: stir a glass of water and then look for the flowing motion. You'll see moving bubbles and perhaps moving specks of dirt, but you won't see the water move. The silvery charge-fluid in a wire has no bubbles or dirt, so even though the charge is visible, we cannot tell if it is moving or still.

Do you still need a definition of "Electric Charge?" I can do no better than the dictionaries: Electric charge is a fundamental property of matter which is the cause of all electrical phenomena. Electric current is a flow of "charge," and when opposite charges are separated, "static electricity" (electrostatic phenomena) appears.

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