AMPERES
A quantity of charge is measured in units called COULOMBS, and
the word Ampere means the same thing as "one Coulomb of charge
flowing per second." If we were talking about water, then
Coulombs would be like gallons, and amperage would be like
gallons-per-second.
What flows inside wires? It has several names:
- Charges of electricity
- Electrons
- Charged atoms (ions in salt water etc.)
- Electric charge
- Electrical substance
- The Electron sea
- Ion population
- The ocean of charge
- Electric fluid
- "Charge-stuff"
Why are Amperes confusing? Simple: textbooks almost always teach
us about amperes and current, but without first clearly
explaining the coulombs and charges! Suppose that we had no name
for "water," and yet our teachers wanted us to learn all about
the mysterious flow inside metal plumbing pipes? Suppose we were
required to understand "gallons-per-second," but we had to do
this without knowing anything about water, or about gallons?
If we'd never learned the word "gallon", and if we had no
idea that water even existed, how could we hope to
understand "flow?" We might decide that "current" was flowing
through dry empty pipes. We might even decide that "current" was
an abstract concept. Or we might decide that invisible
wetness was moving along through the pipes. Or, we could
just give up on trying to understand plumbing at all. Instead we
could concentrate on the math, memorize equations. Do extremely
well on any physics test, but we wouldn't end up with any
gut-level understanding. That's the problem with electricity and
amperes.
We only can understand the electrical flow in wires (the
amperes) if we first understand the stuff that flows inside
wires. What flows through wires? It's the charge, it's the
metal's own particle-sea, the Coulombs...
CHARGE
"Charge" is the stuff inside wires, but usually nobody tells
us that all metals are always jam-packed full of movable
charge. Always. A hunk of metal is like a tank full of water.
Shake a metal block, and the "water" swirls around inside. This
"water" is the movable electric charge found inside the metal.
In our science classrooms we call this by the name "electron
sea," or even "electric fluid." This movable charge is part of
all metals. In fact it's part of all conductors, from plasma to
battery acid to charged dust storms. In copper metal, the
electric fluid is actually the outer electrons of all the copper
atoms. In any metal, the outer electrons do not orbit the
individual atoms. The electrons do not behave as 4th grade
textbook diagrams usually depict atoms. Instead, the atoms'
outer electrons drift around inside the metal as a whole.
The movable charge-stuff within a metal gives the metal its
silvery metallic color. We could even say that charge-stuff is
like a silver liquid. At least it appears silver-colored when
it's in metals. When it's within some other materials, the
movable charges don't usually look silvery. "Silvery-looking
charges" applies to metals, but isn't a hard and fast rule.
Note that this charge-stuff is "uncharged", it is neutral.
It's uncharged charge! Is this even possible? Yes. On average,
the charge inside a metal is neutralized because each movable
electron has a corresponding proton within an atom nearby.
Copper is made up of
free electrons and positive copper ions. Each electron is
always fairly close to a proton. The electric force-fields from
the two opposite charges cancel each other out. The overall
charge is zero because equal quantities of opposite polarity are
both present. For every positive there is a negative. But this
doesn't mean that the charge-stuff is gone. Even though the
average amount of charge inside a metal is cancelled out, we can
still cause one polarity of charge to move along while the other
polarity remains still. For this reason, an electrical current
is a flow of "uncharged" charges. Metal is made of negative
electrons and positive protons; it's like a positive sponge
soaked with negative liquid. We can make this "negative liquid"
flow along.
ELECTRIC CURRENT
Whenever the charge-stuff within metals is forced to flow, we
say that "electric currents" are created. The word "current"
simply means "charge flow." We normally measure the flowing
charges in terms of amperes.
The faster the charge-stuff moves, the higher the amperage.
Watch out though, since amperes are not just the speed of the
charges. The MORE charge-stuff that flows, (flows through a
bigger wire for example,) the higher the amperage. And a fast
flow of charge through a narrow wire can have the same
amperes as a slow flow of charge through a bigger wire. Double
the speed of charges in a wire and you double the current. Pinch
a wire thinner, and the charges in the thin section flow faster,
yet the current stays the same. But if you keep the speed of a
wire's charges constant, and then increase the size of the wire,
you also increase the amperes.
Here's a way to visualize it. Bend a metal rod to form a
ring, then weld the ends together. Remember that all metals are
full of "liquid" charge, so the metal ring acts like a
water-filled loop of tubing. If you push a magnet's pole into
this ring, the magnetic forces will cause the electron-stuff
within the whole ring to turn like a wheel (as if the ring
contained a movable drive-belt). By moving the magnet in and out
of the metal donut, we pump the donut's movable charges, and the
charges flow in a circle. That's essentially how electric
generators work.
Electric generators are magnet-driven charge pumps. The
changing magnetic field pushes the wire's movable sea of
charges, creating the amperes of charge flow, but this can only
occur when a closed ring or "complete circuit" exists. Break the
ring and you create a blockage, since the charges can't easily
escape the metal to jump across the break in the ring. If the
charges within the metal are like a drive-belt, then a gap in
the ring is like a "brake" that grabs the belt in one spot and
stops all belt motion. A complete metal ring is a "closed
electric circuit," while a broken ring is an "open circuit."
A battery is another kind of charge pump. Cut a slot in our
metal ring and install a battery in the slot. This lets the
battery pump the ring's charge-stuff in a circle. Batteries and
generators are similar in that both can pump charge through
themselves and back out again. With a battery installed in our
metal ring, the battery draws charge into one end and forces it
out the other, and this makes the entire contents of the metal
ring start moving. Make another cut in the metal ring, install a
light bulb in the cut, and then the "friction" of the narrow
light bulb filament against the flowing charge-stuff creates
high temperatures, and the wire filament inside the bulb glows
white-hot. The battery drives the ring of charge into motion,
the charge moves along like a solid rubber drive belt, and the
light bulb "rubs" against the moving charge, which makes the
filament grow hot.
Important note: inside wires, usually the charge-stuff flows
extremely slowly; slower than centimeters per minute. Amperes
are an extremely slow, circular flow. See
SPEED OF
ELECTRICITY for info.
WATTS
Watts have the same trouble as Amperes. "Watts" are the name of
an electrical flow... but what stuff does the flowing? Energy! A
"watt" is just a fancy way of saying "quantity of electrical
energy flowing per second." But what is a quantity of electrical
energy? I'll get to that in a sec. But briefly, any sort of
energy is measured in terms of Joules. A joule of electrical
energy can move from place to place along the wires. When you
transport one joule of energy through a channel every second,
the flow-rate of energy is 1 Joule/Sec, and "one Joule per
second" means "one watt." (It might help keep things traight if
you erase all the "watts" in your textbook, and instead write
"joules per second.)
What is power? The word "power" means "energy flow." In order
to understand these ideas, it might help if you avoid using the
word "power" at the start. The word "power" means "energy flow",
so instead you can practice thinking in terms of energy-flow
instead of in terms of the word "power." Also think in terms of
joules-per-second rather than watts, and eventually you'll gain
a good understanding of the ideas behind them. Then, once you
know what you're talking about, you can start speaking in
shorthand. To use the shorthand, don't say "energy flow", say
"power." And say "watts" instead of "joules per second." But if
you start out by saying "power" and "watts", you might never
really learn what these things are, because you never really
learned about the energy flow and the joules.
FLOWING ELECTRICAL ENERGY
OK, what then is electrical energy? It has another name:
electromagnetism. Electrical energy is the same stuff as radio
waves and light. It's made up of magnetic fields and
electrostatic fields. A joule's worth of of radio waves is the
same as a joule of electrical energy. But what does this have to
do with understanding electric circuits? Quite a bit! I'll delve
deeper into this. But first...
How is electric current different than energy flow?
Let's take our copper ring again, the one with the battery and
the light bulb. The battery speeds up the ring of charge and
makes it flow, while the light bulb keeps it from speeding up
too much. The battery also injects joules of electrical energy
into the ring, and the light bulb takes them out again. Joules
of energy flow continuously between the battery and the bulb.
The joules flow almost instantly: at nearly the speed of light,
and if we stretch our ring until it's thousands of miles long,
the light bulb will still turn off immediately when the battery
is removed. (Well, not really immediately. There will
still be some joules left briefly racing along the wires, so the
bulb will stay lit for a tiny instant , until all the energy
arrives at the bulb.) Remove the battery, and the light bulb
goes dark ALMOST instantly.
AMPERES ARE NOT A FLOW OF ENERGY
Note that with the battery and bulb, the joules of energy flowed
one way, down both wires. The battery created the
electrical energy, and the light bulb consumed it. This was not
a circular flow. The energy went from battery to bulb, and none
returned. At the same time, the charge-stuff flowed slowly in a
circle within the entire ring. Two things were flowing at the
same time through the one circuit. There you have the main
difference between amperes and watts. The coulombs of charge are
flowing slowly in a circle, while the joules of energy are
flowing rapidly from an "energy source" to an "energy sink".
Charge is like a rubber drive belt, and electrical energy is
like the 'horsepower' sent between the distant parts of the
belt. Amperes are slow and circular, while watts are fast and
one-way. Amperes are a flow of copper charges, while watts are a
nearly-instant flow of electrical energy created by a battery or
generator. For a better view of this topic, see
WHERE DOES
ENERGY FLOW IN CIRCUITS?
But what are Joules? That's where the electromagnetism
comes in. When joules of energy are flying between the battery
and the bulb, they are made of invisible fields. The energy is
partly made up of magnetic fields surrounding the wires. It is
also made from the electric fields which extend between the two
wires. Electrical-magnetic. Electromagnetic fields. The joules
of electrical energy are the same "stuff" as radio waves. But in
this case they're attached to the wires, and they flow along the
columns of movable electrons inside the wires. The joules of
electrical energy are a bit like sound waves which can flow
along an air hose. Yet at the same time, electrical energy is
very different than sound waves. The electrical energy
flows in the space around the wires, while the electric
charge flows inside the wires.
VOLTS
There is a relationship between amperes and watts. They are not
totally separate. To understand this, we need to add "voltage"
to the mix. You've probably heard that voltage is like
electrical pressure. What's usually not taught is that voltage
is a major part of static electricity, so whenever we deal with
voltage, we're dealing with static electricity. If I grab some
electrons and pull them away from a wire, that wire will have
excess protons left behind. If I place those electrons into
another wire, then my two wires have oppositely-imbalanced
charge. They have a voltage between them too, and a
static-electric field extends across the space between them.
This fields *is* the voltage. Electrostatic fields are
measured in terms of volts per distance, and if you have an
electric field, you always have a voltage. To create voltage,
take charges out of one object and stick them in another. You
always do this when you scuff your shoes across the carpet in
the wintertime. Batteries and generators do this all the time
too. It's part of their "pumping" action. Voltage is an
electrostatic concept, and a battery is a "static electric"
device.
Remember the battery in the copper ring from above? The
battery acted as a charge pump. It pulled charge-stuff out of
one side of the ring, and pushed it into the other side. Not
only did this force the circle of charges to begin moving, it
also caused a voltage-difference to appear between the two sides
of the ring. It also caused an electrostatic field to appear in
the space surrounding the ring. The charges within the copper
ring began moving because they responded to the forces created
by the voltage surrounding the ring. In this way the voltage is
like pressure. By pushing the charges from one wire to the
other, a voltage causes the two wires to become positive and
negative... and the positive and negative wires produce a
voltage. (In hydraulics we would use a pressure to drive water
into a pipe, and because we drove water into a pipe the pressure
in that pipe would rise.)
So, the battery "charged up" the two halves of the copper
ring. The light bulb provided a path to discharge them again,
and this created the flow of charge in the light bulb filament.
The battery pushes charge through itself, and this also forces a
pressure-imbalance in the ring, and forces charges to flow
through the light bulb filament. But where does energy fit into
this? To understand that, we also have to know about electrical
friction or "resistance." Also:
What is Voltage?
OHMS
Imagine a pressurized water tank. Connect a narrow hose to it
and open the valve. You'll get a certain flow of water because
the hose is a certain size and length. Now the interesting part:
make the hose twice as long, and the flow of water decreases by
exactly two times. Makes sense? If we imagine the hose to have
"friction", then by doubling its length, we double its friction.
(The friction always doubles whether the water is flowing or
not.) Make the hose longer and the water flows slower (fewer
gallons per second,) make the hose shorter and the reduced
friction lets the water flow faster (more gallons per second.)
Now suppose we connect a very thin wire between the ends of a
battery. The battery will supply its pumping pressure (its
"voltage"), and this will cause the charge-stuff inside the thin
wire and the charge-stuff within the battery to all start
moving. The charge flows in a complete circle. Double the length
of the wire, and you double the friction. The extra friction
cuts the charge flow (the amperes) in half. The friction is
the "Ohms," it is the electrical resistance. To alter the
charge-flow in a circle of wire, we can change the resistance of
our piece of wire by changing its length. Connect a long thin
wire to a battery and the charge flow will be slow (low amps.)
Connect a shorter wire to the battery and the charge will be
faster (high amps.)
But we can also change the flow by changing the pressure. Add
another battery in series. This gives twice the
pressure-difference applied to the ends of the wire circle...
which doubles the flow. We've just discovered "Ohm's Law:" Ohm's
law simply says that the rate of charge flow is directly
proportional to the pressure difference, and if the pressure
goes up, the flow goes up in proportion. It also says that the
resistance affects the charge flow. If the resistance goes up
while the pressure-difference stays the same, the flow gets LESS
by an "inverse" proportional amount. The harder you push, the
faster it flows. The bigger the resistance, the smaller the flow
(if the push is kept the same.) That's Ohm's law.
Whew. NOW we can get back to energy flow.
VOLTS, AMPS, OHMS, ENERGY FLOW
Lets go back to the copper ring with the battery and bulb.
Suppose the battery grabs charge-stuff out of one side of the
ring and pushes it into the other. This makes charge start
flowing around the whole circle, and also sends energy instantly
from the battery to the light bulb. It takes a certain voltage
to force the charges to flow at a certain rate, and the light
bulb offers "friction" or resistance to the flow. All these
things are related, but how? (Try
bicycle
wheel analogy.)
Here's the simplest electrical relation: THE HARDER THE PUSH,
THE FASTER THE FLOW. "Ohm's Law", can be written like this:
|
VOLTS/OHMS = COULOMBS/SEC |
|
The harder the push, the faster flows the charge
|
|
Note that coulombs per second is the same as "amperes." It
says that a large voltage causes coulombs of charge to flow
faster through a particular wire. But we usually think of
current in terms of amps, not in terms of flowing charge. Here's
the more common way to write Ohm's law:
|
VOLTS/OHMS = AMPERES |
|
Voltage across resistance causes current |
|
Voltage divided by resistance equals current. Make the
voltage twice as large, then the charges flow faster, and you
get twice as much current. Make the voltage less, and the
current becomes less.
Ohm's law has another feature: THE MORE FRICTION YOU HAVE,
THE SLOWER THE FLOW. If you keep the voltage the same (in other
words, you keep using the same battery to power your light
bulb), and if you double the resistance, then the charges flow
slower, and you get half as much current. Increasing the
resistance is easy: just hook more than one light bulb in a
series chain. The more light bulbs, the more friction, which
means that current is less and each bulb glows more dimly. In
the bicycle wheel analogy mentioned above, a chain of light
bulbs is like several thumbs all rubbing on the same spinning
tire. The more thumbs, the slower the tire moves.
Here's a third way of looking at Ohm's law: WHEN A CONSTANT
CURRENT ENCOUNTERS FRICTION, A VOLTAGE APPEARS. We can rewrite
Ohm's law to show this:
|
AMPERES x OHMS = VOLTS |
|
A flow of charge produces a voltage if it encounters
resistance |
|
If resistance stays the same, then the more current, the more
volts you get. Or, if the current is forced to stay the same and
you increase the friction, then more volts appear. Since most
power supplies provide a constant voltage rather than a constant
current, the above equation is used less often. Usually we
already know the voltage applied to a device, and we want to
find the amperage. However, a current in a thin extension cord
causes loss of final voltage, and also transistor circuits
involve constant currents with changing voltages, so the above
ideas are still very useful.
But what about joules and watts? Whenever a certain amount of
charge is pushed through an electrical resistance, some
electrical energy is lost from the circuit and heat is created.
A certain amount of energy flows into the "frictional" resistor
every second, and a certain amount of heat energy flows back out
again. If we increase the voltage, then for the same hunk of
charge being pushed through, more energy flows into the resistor
and gets converted to heat. If we increase the hunk of charge,
same thing: more heat flows out per second. Here's how to write
this:
|
VOLTS x COULOMBS = JOULES |
|
It takes energy to push some charge against the
voltage-pressure |
|
Charge flows slowly through the resistor and back out again.
For every coulomb of charge that's pulled slowly through the
resistor, a certain number of joules of electrical energy race
into the resistor and get converted to heat.
The above equation isn't used very often. Instead, we usually
think in terms of charge flow and energy flow, not in terms of
hunks of charge or hunks of energy which move. However, thinking
in terms of charge hunks or energy hunks makes the concepts
sensible. Once you grasp the "hunks" concepts, once you know
that energy is needed to push each hunk of charge against a
voltage force, afterwards we can rewrite things in terms of amps
and watts. Afterwards we can say that it takes a FLOW of energy
(in watts) to push a FLOW of charge (in amps) against a voltage.
Yet first it's important to understand the stuff that flows.
Think in terms of coulombs of charge and joules of energy.
The charge-flow and the energy-flow are usually written as
amps and watts. This conceals the fact that some quantities of
"stuff" are flowing. But once we understand what's really going
on inside a circuit, it's simpler to write amperes of
charge-flow and watts of energy-flow:
|
VOLTS x COUL/SEC = JOULES/SEC |
|
It takes an energy-flow to make the charge flow
forward against pressure |
|
Don't forget that "Amps" is shorthand for the charge inside
wires flowing per second. And "watts" is shorthand for flowing
energy. We can rewrite the equation to make it look simpler.
It's not really simpler. We've just hidden the complexity of the
above equation. It's shorthand. But before using the shorthand,
you'd better understand the full-blown concept!
|
VOLTS x AMPERES = WATTS |
|
Pushing a current through a voltage requires
energy-flow or "power." |
|
We can get the Ohms into the act too. Just combine this
equation with Ohm's law. Charge flow is caused by volts pushing
against ohms, so let's get rid of amps in the above equation and
replace it with voltage and ohms. This forms the equation below.
Notice: increasing the voltage will increase the energy flow
that's required, but it also increases the charge flow... which
increases the energy flow too! If voltage doubles, current
doubles, and wattage doesn't just double, instead the doubling
doubles too (wattage goes up by four times.) Tripling the
voltage makes the wattage go up by NINE times. Write it like
this:
|
VOLTS x (VOLTS/OHMS) = WATTS |
|
Voltage applied across ohms consumes a constant flow
of electric energy |
|
So, if you double the voltage, energy flow increases by four,
but if you cut the friction in half while keeping voltage the
same, energy flow goes up by two, not four. (The amperes also
change, but they're hidden.)
Here's one final equation. It's almost the same as the one
above, but voltage is hidden rather than ampereage:
|
(AMPERES x OHMS) x AMPERES = WATTS |
|
When charge flows against ohms, electrical energy is
being used up |
|
So, the watts of energy flow will go up by four if you double
the current. But if you can somehow force the current to stay
the same, then when you double the friction in the circuit, the
energy flow will only double (and the voltage will change, but
that part's hidden.)
And finally, here are a couple of things which can mess you
up. Think about flowing power. Try to visualize it. I hope you
fail! Remember... POWER DOESN'T FLOW! The word "power" means
"flow of energy." It's OK to imagine that invisible hunks of
electrical energy are flowing across a circuit. That's sensible.
Electrical energy is like a stuff; it can flow along, but
"energy flow" cannot flow. Power is just flowing energy, so
"power" itself never flows. Beware, since many people (and even
textbooks) will talk about "flows of power." They are wrong.
They should be talking about flows of electrical energy. That
drives home the fact that energy can flow from place to place,
and the flow-rate is called "power." "Flow of power" is a
confusing, wrong, (and fundamentally stupid) concept.
Guess what. The same books and people who talk about "flows
of power" will also talk about "flows of current." They'll try
to convince you that "current" is a stuff that can flow through
wires. Ignore them, they're wrong. Yes, elecric charge is like a
stuff that exists inside all wires, but current isn't like that,
current is different. When pumped by a battery or a generator,
the wire's internal charge-stuff starts flowing. We call the
flow by the name "an electrical current." But there is no such
STUFF as "current." Current cannot flow. (Ask yourself what
flows in rivers, current... or water? Can you go down to the
creek and collect a bucket of "current?") If you want a big
shock, read through a textbook or an electronics magazine and
see how many times the phrase "current flow" appears. Like the
phrase "power-flow," it's not just wrong, it's STUPID. Authors
are trying to teach us about flows of charge, but instead they
end up convincing us that "current" is a kind of stuff! It's so
weird. And it's a bit frightening because it's so widespread.
It's very rare to find a book which avoids the phrase "current
flow" and explain charge-flow. Most books instead talk about
this crazy flow of "current." It's been going on so long that
engineers speak of "current carriers" when they're talking about
charge carriers, and they use a law they call "conservation of
current," when of course current isn't conserved, only charge is
conserved. So, it's no wonder that students have trouble
understanding electricity. They end up thinking that water-pipes
must be utterly different from circuits because you can fill a
glass with water, but who on earth can imagine filling a
container with "current?" Fortunately circuits really are like
water pipes, and its buckets of charge you want to discuss, not
buckets full of "current."
OK, I've run out of steam for now. Ooo! Ooo! No I haven't. I
must now go on a crusade about
How Capacitors Are
Explained Wrong. Then I'll go on and on about
Why most
explanations of transistors basically suck.
LINKS
http://amasci.com/elect/vwatt1.html
Created by Bill Beaty.
Mail me at:
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