The Big List
WHAT IS "ELECTRIC CHARGE?"
What is electric charge? Well, there's an easy answer and a hard
Here is the easy answer:
1999 W. Beaty BSEE
...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
...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
the stuff that, when it wiggles fast, creates light.
the stuff that, when it wiggles slower, creates radio waves.
the stuff that, when it wiggles very slowly, creates energy in electric circuits.
the stuff that, when it flows or spins, creates magnetism.
the stuff that reflects light and makes objects visible.
the stuff that makes metals look metallic or "silvery."
the stuff that causes electrical attraction and holds everyday objects together.
the stuff inside of wires that is movable, almost fluid.
the stuff inside of nonconductors that is immobile and "frozen" in place.
the stuff that is measured in units called Coulombs.
the stuff that scientists once called "quantity of electricity" and "particles of electricity."
THE LESS-EASY ANSWER
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
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
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
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
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.