Understanding the Simple Mysteries of Electricity
A fluidly fluent approach
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HOW ARE WATTS,
OHMS, AMPS, and VOLTS RELATED?
What's all
this about Watts, Volts, and Amps? Good question. Some info is below, and
more can be found at:
But
none of these links give a direct answer to the question. Be warned! A useful
answer is going to be HUGE! (grin)
Here's the
extremely short answer...
Conductive
objects are always full of movable electric charges, and the overall
motion of these charges is called an 'electric current.' Voltage can cause
electric currents because a difference in voltage acts like a difference in
pressure which pushes the conductors' own charges along. A conductor offers a
certain amount of electrical resistance or "friction," and the
friction against the flowing charges heats up the resistive object. The
flow-rate of the moving charges is measured in Amperes. The transfer of
electrical energy (as well as the rate of heat output) is measured in Watts.
The electrical resistance is measured in Ohms. Amperes, Volts, Watts, and
Ohms.
Not
so simple? Then let's take a much deeper look. First the watts and amperes.
Watts and amps are somewhat confusing because both are flow-rates, yet we
rarely talk about the "stuff" which does the flowing. I suspect
it's impossible to understand a flow rate without first understanding the
substance which flows. Take water flow for example, could we really
understand gallons-per-second, if we didn't understand gallons, and we had never
touched water? It's not easy to understand flow rates like Amperes or Watts
without understanding the "flowing material." First let's do the
Amperes.
Since a current is a flow of charge, the common expression
"flow of current" should be avoided, since literally it means
"flow of flow of charge."
- Modern College Physics. Sears,Zemanski,Richards,Wher
Current
isn't a stuff. Electric currents are the flows of a stuff. OK then,
what's the name of the stuff that flows during an electric current? The
flowing stuff is called "Charge." |
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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
- 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," yet our teachers wanted us
to learn all about the mysterious flow inside metal plumbing pipes? Suppose
we're 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 and 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
copper, 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 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. 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. But if you keep the speed of a wire's charges
constant, 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
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
Let’s
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 COULOMBS/SEC = JOULES/SEC It takes a flow of energy to make 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 uses up a constant flow of electrical 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:
(AMPERESxOHMS) x AMPERES = WATTS When charge is flowing 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, sincemany people (and even
textbooks) will talk about "flows of power." They are wrong. They
should be talking about flows of electrical energy. "Flow of power"
is a 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. Elecric charge is like a stuff that exists inside all wires, but
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 no wonder that
students have trouble understanding electricity. They essentially think that
waterpipes are totally different from circuits because you can fill a glass
with water, but who on earth can imagine filling a container with
"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.
From Amasci @ http://amasci.com/elect/vwatt1.html
For more info about
electromagnetism see http://nexusilluminati.blogspot.com/search/label/electromagnetism
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