# Confused about "What is current flow"

Discussion in 'Electronic Basics' started by Brian, Aug 23, 2003.

1. ### BrianGuest

A very simple approach:
Let's say that we have a battery with a resistor connected across it. Let's also
say that the wire that connects the resistor to the battery, has a diameter of
one atom. At the positive end of the battery, the battery terminal pulls one
electron away from the atom at the end of the wire. That atom then becomes
positive charged. This positive charged atom, then pulls an atom away from the
atom next to it (that is closer to the negative terminal of the battery).
Through chain reaction, this positive charge works it's way to the negative
terminal of the battery (which is called conventional current). The electron
that is pulled from each atom, is called electron current.
Hope this helps,
Brian

2. ### Jeff StephensGuest

Many years ago I attended the Navy's electronics technician school at
Treasure Island, CA.
I was taught that current flow is the flow of electrons from the negative
terminal of the battery
(or any power supply source) to the positive terminal. I also remember that
the instructor
briefly mentioned something called "conventional current" which he said was
a theory that
said that current is really an "effect" that is opposite to the direction of
electron flow. This was
basically, as far as I can remember, all that was said on this subject, and
the course proceeded
for the remainder of the 38 weeks it lasted, to treat electron flow and
current flow as synonomous.

Now I am studying a book which contains the following passages:

v = iR Eq. 1

"Equation 1 implies a specific relation between reference directions for
voltage and
current. This relation is show explicitly as:

i R
------>
-------/\/\/\/\/\/\/\-------
+ v -

the arrow defines the positive flow of current (flow of positive
charge) is directed * in *
at the resistor terminal assigned to be positive voltage. This
convention is generalized
to an arbitrary element as follows:

i
----<-------
| +
|
-------
| | v
-------
|
| -
--------------

The variables v and i are called the terminal variables for the
element. Note that the
values of each of these variables may be positive or negative
depending on the actual
direction of current flow or the actual polarity of the
voltage."

I am completely confused by this passage and subsequent ones which depend on
it. My poor
mind is fixated on what I learned in my younger days, i.e., that current
flow IS the flow of
electrons out of the NEGATIVE terminal of the source and into the POSITIVE
terminal of
the source, which, of course, results in the following:

i R
------>
--------/\/\/\/\/\/\/\---------
- v +

which is the reverse of what the book shows. The book's statement about
"flow of postive
charge" is really confusing because positive charges are protons and they
certainly don't flow
unless you split the atom. I guess most students today are taught this
convention from the git-go
and so they don't have to unlearn the previous convention. Can someone
explain this new
way of thinking about current flow to me, or perhaps point me to some
website that does so.
Thanks.

Regards,
Jeff S

3. ### Kevin AylwardGuest

Once upon a time people thought that current was a flow of electrons
from positive to negative. They were wrong, but we still pretend that's
the way it is. That's it. There's nothing more to understand on the
matter.

It doesn't make any odds what way you say they flow, it all cancels out.
If what is black is really white, but everyone calls everything that is
black is white, there is no net difference.

There is no current "flow". "Current" already contains the notion of
flow. Current means "flow of charge".

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

4. ### Mark HaaseGuest

For the OP's sake:

http://www.ibiblio.org/obp/electricCircuits/DC/DC_1.html

Some experimenters speculated that invisible "fluids" were being
transferred from one object to another during the process of rubbing,
and that these "fluids" were able to effect a physical force over a
distance. Charles Dufay was one the early experimenters who
demonstrated that there were definitely two different types of changes
wrought by rubbing certain pairs of objects together. The fact that
there was more than one type of change manifested in these materials was
evident by the fact that there were two types of forces produced:
attraction and repulsion . The hypothetical fluid transfer became known
as a charge .

One pioneering researcher, Benjamin Franklin, came to the conclusion
that there was only one fluid exchanged between rubbed objects, and that
the two different "charges" were nothing more than either an excess or a
deficiency of that one fluid. After experimenting with wax and wool,
Franklin suggested that the coarse wool removed some of this invisible
fluid from the smooth wax, causing an excess of fluid on the wool and a
deficiency of fluid on the wax. The resulting disparity in fluid
content between the wool and wax would then cause an attractive force,
as the fluid tried to regain its former balance between the two
materials.

Postulating the existence of a single "fluid" that was either gained or
lost through rubbing accounted best for the observed behavior: that all
these materials fell neatly into one of two categories when rubbed, and
most importantly, that the two active materials rubbed against each
other always fell into opposing categories as evidenced by their
invariable attraction to one another. In other words, there was never a
time where two materials rubbed against each other both became either
positive or negative.

Following Franklin's speculation of the wool rubbing something off of
the wax, the type of charge that was associated with rubbed wax became
known as "negative" (because it was supposed to have a deficiency of
fluid) while the type of charge associated with the rubbing wool became
known as "positive" (because it was supposed to have an excess of
fluid). Little did he know that his innocent conjecture would cause
much confusion for students of electricity in the future!

5. ### MantraGuest

It *is* just a convention, but there is a reason: the algebra of
doing circuit analysis tends to be less confusing - you'll have a
higher likelihood of a spurious "-"s that wreak your calculation when
you analyze with negative electron flow. Positive or negative, the
calculations all turn out the same, but only *if* don't accidently
flip any voltage drops in a loop.

MM

6. ### Animesh MauryaGuest

Electronics teachers and authors of textbooks are often chided for
passing on an error to their students: the false idea that electric
current is a flow of positive particles in one direction, when it
really is a flow of negative electrons in the opposite direction.
In fact, those who do the chiding are themselves mistaken. They are
laboring under the misconception that "electricity" is invariably made
of negatively-charged particles called electrons. This is wrong, and
it leads people to wrongly conclude that electric current is really a
flow of negative particles. Actually, in some situations, electric
current can really be a flow of positive particles. In other
situations, the flow is negative particles. And sometimes it's both
positive and negative flowing at once.
"Electricity" is not made of electrons (or to be more specific,
Electric Charge, which is sometimes called "Quantity of Electricity,"
is not made of electrons.) It actually comes in two varieties,
positive and negative particles. In the everyday world of electronics,
these particles are electrons and protons.
Because the negative particles carry a name that SOUNDS like
"electricity," people unfortunately start thinking that the electrons
ARE the electricity, and that protons (having a much less electrical
name?) are not. Some text and reference books even state this
outright, saying that electricity is composed of electrons. In reality
the electrons and protons carry electric charges of equal strength. If
electrons are "electricity", then protons are "electricity" too.
Now everyone will rightly tell me that the protons within wires cannot
flow, while the electrons can. Yes, this is true of solid metals.
Metals are composed of positively charged atoms immersed in a sea of
movable electrons. When an electric current is created within a copper
wire, the "electron sea" moves forward, but the protons within the
positive atoms of copper do not.
However, SOLID METALS ARE NOT THE ONLY CONDUCTORS, and in many other
substances, the positive atoms *do* move, and they *do* participate in
the electric current. These various non-electron conductors are
nothing exotic. They are all around us, as close to us as they
possibly can be.
For example, if you were to poke your fingers into the anode/flyback
section inside a television set, you would suffer a dangerous or
lethal electric shock. During your painful experience there obviously
was a considerable current directed through your body. However, NO
ELECTRONS FLOWED THROUGH YOUR BODY AT ALL. The electric charges in a
human body are entirely composed of charged atoms. During your
electrocution, it was these atoms which flowed along as an electric
current. The electric current was a flow of positive sodium and
potassium atoms, negative chlorine, and numerous other more complex
positive and negative molecules. During the electric current, the
positive atoms flowed in one direction, while the negative atoms
simultaneously flowed in the other. Imagine the flows as being like
crowds of of tiny moving dots, with half the dots going in one
direction and half in the other. The crowds of little dots move
through each other without any dots colliding.
So, in this situation, which direction did the electric current REALLY
have? Do we follow the negative particles and ignore the positive
ones? Or vice versa?
Batteries are another example of a non-electron or "ionic" conductor.
When you connect a light-bulb to a battery, you form a complete
circuit, and the path of the flowing charge is *through* the inside of
the battery, as well as through the light bulb filament. Down inside
the battery, within the wet chemicals between the plates, the electric
current is a flow of both positive and negative atoms. There is a
powerful flow of electric charge going through the battery, yet no
electrons flow through the battery at all. What is the real direction
of the electric current while it's between the two plates of the
battery? Not right to left, not left to right, but in both directions
at once. Out in the metal wires, the flow is from negative to
positive. But inside the battery's wet electrolyte, the charge-flow is
in two opposite directions at the same time.
There are many other places where this kind of positive/negative
charge flow can be found. Electric charges in the following list of
devices and materials are a combination of movable positive and
negative particles. During an electric current, both varieties of
particles are flowing past each other in opposite directions.
TWO-WAY POS/NEG ELECTRIC CURRENTS CAN EXIST IN:
• batteries
• human bodies
• all living organisms
• the ground
• the ocean
• electrolytic capacitors
• aluminum smelters
• liquid mercury
• ion-based smoke detectors
• Geiger counter tubes
• electroplating tanks
• electrophoresis gels in medicine (esp. DNA testing)
• air cleaners, smoke precipitators
• particle beams
• the vertical "sky current" in the atmosphere
• gas discharges, which include:
• electric sparks
• flourescent tubes
• neon signs
• the Aurora
• lightning and corona discharges
• arc welders
• thyratron tubes
• mercury vapor rectifiers
• sodium and mercury arc streetlights
The above list of conductors which contain both positive and negative
flows is not short. Again I ask you, what is the REAL direction of
electric current? We cannot solve the problem by belittling it, or by
pretending that it pertains only to something exotic, to something not
part of everyday life.
Let's get down to the details of the problem. When trying to
understand electric circuits and electrical measurements, how can we
make measurements of the important entity named Electric Current?
Won't we first have to figure out how much of the current is composed
negative particles going one way and positive the other? Yes, but only
if we want to know everything about the electric current. The negative
and positive flows are usually not equal, and the speed of the
positives in one direction is usually not the same as the speed of the
negatives in the other. However, there is a nasty trick we can pull
which avoids having to look at the particles at all...
The main effects produced by electric current are magnetism, heating,
and voltage drop across resistive conductors. These three effects
don't care about the amounts of positive and negative particles, or
about their speed, mass, charge, etc. If a hundred positive particles
flow left per second, this gives just as much magnetism, heating, and
voltage drop as a hundred negative particles flowing to the right per
second. (Note: this is because reversing the polarity of the particles
reverses the current, and reversing the particle flow direction
reverses the reversed current!) Magnetism, heating, and voltage drop
together represent nearly every feature that is important in everyday
electrical circuitry. And so as far as most electrical devices and
circuits are concerned, it makes no difference if the current is
positive particles going one way, negative particles going the other,
or half as many negatives flowing backwards through a crowd of half as
many positives.
So, to simplify our measurements and our mental picture of Electric
Currents, we cut away the unused parts of the picture. We
INTENTIONALLY DEFINE the electric current as being a flow of
exclusively positive particles flowing in one particular direction. We
don't care about the real polarity of the particles. We don't care
about their speed, and we don't care about their number. We ignore the
chemical effects and the effects of the velocity and direction moving
particles. We ignore the collisions between positive and negative
particles. All we care about is the total charge which moves past a
particular point in the circuit. The real charges are too complicated
to deal with, and the added complexity gets us very little
information, as long as we're only interested in voltage drop,
magnetic fields, and heating.
Once we start ignoring the speed and direction of the charges, we can
then build electrical instruments, "amp meters," which measure the
electric current in terms of the magnetism it creates, or by the
voltage drop which appears across a resistor, or by the temperature
rise being created in a calibrated piece of resistance wire. These
three types of meter will agree that "current" is "current," then we
can use these meters everywhere. In nearly every situation they will
tell us all we could ever want to know about flows of charged
particles in any circuit. An amp-meter might not be appropriate when
used in an exotic physics experiment. But for more than 99% of
electricity and electronics, the direction of the particles is
irrelevant, and an ammeter tells us the "real" current.
We do cause some problems in choosing to simplify "Electric Current"
in this way. For example, what if we think in terms of simplified
electric current for many, many years? Couldn't we all eventually come
to believe that this oversimplified concept of electric current is
REAL? Yet it's not real, it is simply one aspect of flowing particles.
For this reason, we might start to see "Electric Current" as a sort of
abstract, invisible, difficult-to-visualize thing. We might lose track
of the facts that electric current is an actual flow of matter, or
that there are real, visible particles flowing along inside that
circuit, or that they have a particular average speed, mass, and
direction.
Because it is so incredibly useful, the simplified interpretation of
Current takes over and becomes more real than the real world. It is
incredibly useful, and it lets us understand parts of physical science
which otherwise might be too complicated to think about. But in
letting it take over, some nagging questions are left behind, such as

"WHICH WAY DOES THE ELECTRICITY REALLY FLOW?"

Animesh Maurya

7. ### Kevin AylwardGuest

No its not short, but is not really relevant in the context of electric
circuits. If we are dealing with general purpose electronics, in the
majority of cases, we are discussing electron flow.

Again I ask you, what is the REAL direction of
This is not really sufficient. Charge flow is not just a flow of matter
particles. If this were so, the ammeter placed in a capacitor would read
zero under AC conditions. Charge is a net effect of photon movement, it
is not restricted to residing within a charged particle.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

8. ### Roger JohanssonGuest

The best article I have ever read on this issue.

Should be saved and used in a FAQ for this newsgroup, on web sites for
beginners and used whenever the issue comes up.

You are a very good writer.
The only (positive) criticism I can give you is that you could insert
more empty lines here and there, to break up the text into smaller
blocks, to make it even easier to read.

9. ### Fred AbseGuest

Would that be wheat or rye?
All the above refer to ions, which are charged atoms, ie atoms having an
excess or deficiency of electrons. It can be argued that the ions
constitute a conductor, in which the current still consists of electron
flow. Experience tends to bear this out, since current flows just as fast
in an ionized medium as it does in a "conventional" conductor, whist ions
move relatively slowly. remember "ion traps" in older CRTs?

-
Then there's duct tape ...
(Garrison Keillor)

10. ### Fred AbseGuest

Why? If you just change the convention so that negative becomes positive
and vice versa, the math's the same.

The math doesn't know about electrons, electrons don't do math

11. ### Wim LewisGuest

Actually, electrons don't move very quickly in a conventional conductor,
either. Certainly not as fast as the change in voltage propagates
through the conductor. The electric *field* propagates quickly, but
the individual charge-carriers move much more slowly.

Take an analogy of electrical wiring being like plumbing. Now imagine
you're in the bathroom and you turn the shower on, drawing hot water
from the water heater. Water starts flowing out of the shower head
immediately, and (nearly) simultaneously, starts flowing into the
other end of the pipe, from the water heater. But it takes
several seconds for the water coming out of the shower head to
become hot. Why is this? Why should it take several seconds for
the hot water to arrive even if the water-current starts flowing
out of the water heater immediately? It's because the *change in
water pressure* caused by turning the tap on moves through the
pipe much more quickly than the actual *water* does.

It's the same with electricity. Change in voltage moves quickly --- at
the speed of light, or a bit slower if you include transmission-line
effects. But the electrons (or ions, or whatever is transferring the
charge) typically move much more slowly than that.

(If you really want to, you can calculate the average electron
velocity --- the drift velocity --- from the density of electrons
in the material, the charge per electron, and the current (charge
per second):
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html )

As for the original question: I usually think of current as the
flow of positive charge, without worrying too much about what's
carrying the charge. As it happens, the most common charge carriers
are electrons, and since they have negative charge, they move in
the opposite direction to the current. Kind of like if I want to
give a company some money in return for goods: I could hand them
some cash (positive charge), or they could send me a bill. The bill
represents a debt, a "negative charge" of money, and it moves in
the opposite direction to the "money flow".

12. ### Animesh MauryaGuest

You said that potential difference is established almost at the speed
of light across a conductor. We further know that potential difference
is necessary for the flow of current.

If we define electric current in a metallic conductor as a flow of
electron then there must exist some phase difference between voltage
and current.

Current must be lagging as the drift velocity is very-very small. But
we know that in a pure conductor voltage and current are in same
phase.

Animesh Maurya

13. ### RatchGuest

Sure, drift velocity is small, but all the charge carriers from one end
of the conductor to the other move at just about the same time. Therefore
current exists at the speed of light difference between the ends of the
conductor.

By the way, current is charge flow. Therefore "current flow" is
actually charge flow flow, which is a redundant phrase. If you talk about
current, which already means charge flowing, say that it exists, not that it
flows. If you want to use the word "flow", then say charge flows. Ratch

14. ### Kevin AylwardGuest

Actually, this is not correct. Charge flow runs similar to mass flow,
that is things continue to keep moving in a straight line unless acted
upon by a force etc. If you start accelerating a charge, and then turn
of the voltage it keeps moving. In fact, superconductors illustrate
this.
Yes.

The current, accepted theory of EM is quantum electrodynamics, qed. This
explains *all* EM effects by the exchange of photon momentum between
charges. The net effect of this momentum exchange is dependant on the
distance between charges. If an electron starts to move nearer to
another one, the electrons will react to this effect at the speed of the
photons, i.e. light. One can argue that charge flow, is the cumulative
effect of photon motion. That is, it is a number that summarises the net
backwards and forwards momentum flow of photons. That is, there is not
such a thing as a real object actually flowing in a way mass would flow.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.