Oooo, good question. Some info is at
ELECTRICITY FAQ, also
Electricity is not energy and
Electricity Misconceptions. But none of these have a direct
answer to your question. A useful answer is going to be HUGE. Be warned!
Here's the extremely short answer. Voltage pushes charges through an
object which has electrical resistance, and this heats up the resistive
object. The flow of the charges is measured in amperes, the flow of
electrical energy and heat output is measured in watts, and the resistance
is measured in ohms.
First the watts and amperes. These are somewhat confusing because they
are the names of flows, but we never talk about the STUFF that flows.
Electric current isn't a
stuff, electric current is the flow of a stuff. What is the name
of the stuff? Charge.
What flows in wires?
A quantity of charge is measured in units called COULOMBS, and the
word "ampere" means the same thing as "coulomb of charge flowing per
second." Why do I say that amperes are confusing? Well, suppose we had
no name for water, yet our teachers wanted us to learn about "fluid flow".
Suppose we all had to learn about "gallons-per-second," but without
knowing anything about gallons, or about water, or about the very idea of
"liquids." If you'd never learned the word "gallon", and if you had no
idea that water even existed, how could you understand "currents?"
That's the problem with electricity and amperes.
We can only understand the flow (the amperes) if we first understand the
stuff that flows in wires: the charge, the coulombs.
"Charge" is the stuff inside wires, but usually nobody tells us that ALL
METALS are full of charge. Always. A hunk of metal is like a tank full
of water, and the "water" is the movable electric charge inside it. In
physics classes we
call this "the electron sea" or even "electric fluid." This charge is
part of all
metals. In copper, the electric fluid is the outer electrons of all the
The movable charge-stuff within metals gives them their silvery
color. We could even say that charge-stuff is like a silver liquid (at
least it's silvery when it's inside metals.)
Note that this charge is "uncharged", it is neutral. Is this impossible?
No. The charge inside of metals is neutral because each electron has a
corresponding proton nearby, and the fields from the opposite charges
cancel out. The charge is cancelled, but this doesn't mean that the
charge-stuff is gone! Even though the charge inside a metal is cancelled
out, we can still force it to flow along. We can make the metals own
electrons flow past its protons.
When the charge-stuff within metals is forced to flow, electric currents
are created. We measure the currents in terms of amperes. The faster the
charge-stuff moves, the higher the amperage. Also, the MORE charge-stuff
that flows (through a bigger wire) the higher the amperage. A fast flow
of charge through a narrow wire can be the same current as a slow flow of
charge through a bigger one.
Here's a way to visualize it. Bend a metal rod to form a ring, and weld
the ends together. Remember that all metals are full of "liquid" charge.
If you push a magnet's pole into this ring, the
magnetic forces will cause the electron-stuff within the ring to turn like
a wheel (as if the ring contained a movable drive-belt). By moving the
magnet, we pump the charges, and the charges flow. That's how electric
Generators are magnet-driven charge pumps. The moving
magnetic fields push the wire's charges, creating
the amperes, but this only occurs when a complete circuit is present.
Break the ring and you create a blockage, since the charges can't easily
jump across the break in the ring. A complete ring
is a simple electric circuit. Cut the ring and install a battery in
the cut, and the battery can pump the ring's charge-stuff in a circle.
Make another cut, install a light bulb, and the "friction" of the narrow
filament against the flowing charge-stuff creates high temperatures, and
the wire filament inside the bulb glows white-hot.
Important note: the charge-stuff flows extremely slowly through the wires,
slower than centimeters per minute. Amperes are an extremely slow,
circular flow. See SPEED OF ELECTRICITY
"Watts" have the same trouble as amperes. They are the name of an
electrical flow, but what 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 energy? Quantities of energy are measured in
Joules. A joule of electrical energy can move from place to place along
the wires. When you
transport one joule through a channel every second, the flow-rate of
energy is 1 Joule/Sec, and "one Joule per second" means "one watt."
What is power? The word "power"
means "energy flow." It might help you to avoid thinking about "power"
at the start. If you first practice thinking in terms of energy flow
instead of power, and
joules per second instead of watts, eventually you'll gain a good
understanding. Once you know what you're talking about, then
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 begin by saying "power" and "watts", you might never
really learn what these things are, because you never really learned about
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 is
composed of magnetic fields and electrostatic fields. A joule of radio
waves is the same as a joule of electrical energy. What does this have
to do with understanding electric circuits? Quite a bit! But I'll come
back to this later.
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 injects joules of energy into the ring, and the light
bulb takes them out again. Joules of energy flow between the battery and
the bulb. They flow 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 IMMEDIATELY.
There will still be some joules moving along the wires, so the bulb will
stay on for a tiny fraction of a second, until all the energy
arrives. Remove the battery, and the light bulb goes dark ALMOST
AMPERES ARE NOT A FLOW OF ENERGY
Note that the joules of energy flowed ONE WAY, down BOTH wires. The
battery created them, and the light bulb consumed them. 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
ring. There you have the difference between amperes and watts. The
coulombs flow slowly in a circle, while the joules flow rapidly from an
"energy source" to an "energy sink". Amperes are slow and circular, while
watts are fast and one-way. Amperes are a flow of copper charges, while
watts are a flow of energy created by a battery or generator.
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 fields. The energy is partly made up of magnetic fields
wires. It is also made from the electric fields which extend between the
The electrical ENERGY flows in the space around the wires, while
CURRENT flows inside the wires.
There is a relationship between amperes and watts. They are not totally
separate. To understand this, we need to add "voltage". You've
voltage is like electrical pressure. What's usually not taught is that
voltage is part of static electricity. If I grab electrons from a wire,
that wire will have excess protons left behind. If I place those
another wire, then my two wires have oppositely imbalanced charge. They
have a voltage
between them too, and a static-electric field extending across the space
between them. THIS FIELD IS THE VOLTAGE. Electrostatic fields are
measured in terms of volts/distance, and if you have a field, you always
have a voltage. To create voltage, take charges out of one object and
stick them in another.
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. This caused a voltage-difference to appear
the two sides of the ring. It also caused an electrostatic field to
appear in the space surrounding the ring. And finally, it caused the
charge-stuff inside the light bulb filament to begin flowing. 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. 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 charge to flow through the
light bulb filament. But where does energy fit
into this? To understand that, we have to know about electrical friction
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. (This happens whether the water is flowing or not.)
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 of the thin wire to start moving. Double the
length of the wire, and you double the friction. The extra cuts the
flow (the amperes) in half. THE FRICTION IS THE "OHMS", IT IS THE
ELECTRICAL RESISTANCE. To change the charge-flow, we can change the
resistance of our pice of wire by changing its length. 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 wire ends. Which
doubles the flow. We've just discovered "Ohm's Law", which says that the
flow is directly proportional to the pressure difference, and if the
pressure goes up, the flow goes up in proportion. It also ways that if
resistance goes up, the flow goes DOWN by a 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 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 charges flow around the circle, and also sends energy
to the light bulb. It takes voltage to force the charges to flow, and the
light bulb offers "friction" or resistance to the flow. All these things
are related, but how? (Try bicycle wheel
Here's the simplest electrical relation: THE HARDER THE PUSH, THE FASTER
THE FLOW. This is called "Ohm's Law", and we can write it like
VOLTS/OHMS = COULOMBS/SEC
It says that a large voltage causes coulombs of charge to flow faster
through the wire. But we usually think of current in terms of amps, not
in terms of flowing charge. Here's the common way to write Ohm's law:
VOLTS/OHMS = AMPERES
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 too: THE MORE FRICTION YOU HAVE, THE SLOWER
THE FLOW. If you keep the voltage the same (in other words, 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 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.
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
AMPERES x OHMS = VOLTS
The more current, the more volts you get. Or, if the current is forced to
stay the same and you increase the friction, 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 know
the voltage, and we want to find the amperage. However, transistor
circuits involve constant currents, so the above ideas are very useful.
But what about watts? When charge is being pushed through an electrical
resistance, electrical energy is lost and heat is created. A certain
amount of energy is flowing into the resistor device every second. If we
increase the voltage, more energy flows into the resistor and gets
converted to heat. If we increase the flow of charge, same thing: more
heat flows out per second. Here's how to write this:
VOLTS x COULOMBS/SECOND = JOULES/SECOND
For every coulomb of charge that's driven through the resistor, a certain
number of joules of electrical energy flow into the resistor and they flow
out as heat.
The charge flow and the energy flow are usually written as amps and watts.
This conceals the fact that quantities of "stuff" are flowing. But once
you understand what's really going on inside a circuit, it's simpler to
write amperes of charge flow and watts of energy flow. IF WE INCREASE THE
VOLTAGE, THE CHARGE FLOW INCREASES, AND THE ENERGY FLOW INCREASES EVEN
MORE. Doubling the voltage-pressure caus
VOLTS x AMPERES = WATTS
We can get the Ohms into the act too. Just combine this equation with
Ohm's law. If you increase the voltage, it increases the flow of charge
through the electrical friction device. But since voltage AND current
both get larger at the same time, the energy flow increases even more. If
voltage doubles, current doubles, and wattage doesn't just double, instead
the doubling doubles too (wattage goes up by four.) Write it like this:
VOLTS x VOLTS / OHMS = WATTS
So, if you double the voltage, energy flow increases by four, but if you
the friction while keeping voltage the same, energy flow gets cut in half
(not in 1/4.) The amperes
change too, but they're hidden. Here's one final equation. It's the same
as the one above, but voltage is hidden rather than ampereage:
AMPERES x AMPERES x OHMS = WATTS
So, the watts of energy flow will go up by four if you double the
current. But if somehow you can force the current to stay the same, then
when you double the friction the energy flow will double (and the voltage