Which Way Does Electricity Flow?
Electrons go one direction while the positive charges seem to go the other. Which is correct?
By Douglas Krantz
The negatively charged electrons are drawn toward the positively charged battery terminal, or the next positively charged atom. The electrons move.
As an electron leaves the atom and is replaced with another electron, each atom changes from a neutral charge to a positive charge and back again. The atoms of a wire themselves, however, do not move.
Because the protons in the nucleus of the atom don't move, the protons don't affect the movement of electrical charges or the magnetic fields; because the electrons move, the electrons affect the electrical charges and magnetic fields.
So... In a wire, negatively charged electrons move, and positively charged atoms don't.
Electrical engineers say that, in an electrical circuit, electricity flows one direction: out of the positive terminal of a battery and back into the negative terminal. Electronic technicians say that electricity flows the other direction: out of the negative terminal of a battery and back into the positive terminal.
These two theories seem to be in conflict. Where'd this confusion over the direction of electrical flow come from?
The Discovery of Electrical Flow
Benjamin Franklin started the confusion. He rubbed wool and wax together and noticed what we call static electricity.
At that time, nobody knew about electrons or charges, but trying to explain the observed phenomena, he concluded that something moved from either the wax to the wool, or from the wool to the wax. It looked to him like something moved from the wax to the wool.
He published the discovery.
The Establishment of the Direction of Flow
Around the world scientists and engineers alike added their own ideas to this theory, held discussions on this theory, published their findings using this theory, and formally established that, for electrical current, this was the direction of flow.
In the scientific and engineering world, and in all the literature and books, everyone "knew" that in a circuit, electricity flowed from the positive battery terminal to the negative terminal. This was a well-established concept and any change to that concept would cause mass pandemonium.
But the confusion over electrical flow direction started anyway.
In 1869, using high voltage, German Physicist Johann Hittorf noticed a phenomenon of waves or rays emanating from the cathode in a vacuum tube. Later these rays or waves became known as cathode rays.
With the battery this way, when the filament was hot, negatively charged electrons boiling off the filament would migrate to the positively charged plate. If the battery was reversed so was positive and the plate was negatively charged, no electrons would travel from the plate because cool a plate does not emit electrons.
Some years later, on hearing about these rays, and while trying to understand and prevent some blackening on the inside of incandescent lamps, Thomas Edison had one of his assistants place an extra electrode inside a lamp.
It was discovered that if a battery, with its positive side connected to the added electrode (plate), and its negative side connected to the filament (cathode), an electrical current would flow. If the battery was connected the other way around, it was also observed that no current would flow.
This current, flowing from the hot filament, through the vacuum, to the electrode, was invisible. No practical purpose could be found for the discovery, but Edison patented this "Edison Effect" anyway.
Years later, J.J. Thomson investigated the cathode rays and he figured out about the electron in the atom. He also concluded that the current flow known as the "Edison Effect" was made by electrons traveling through the vacuum.
The Conflict in the Direction of Electrical Flow
We had a conflict. The theories and books all said that in a circuit, electrical current flows out of the positive terminal of a battery, and returns into the negative terminal. These discoveries concluded that, contrary to conventional wisdom, electrons flowed the other direction.
Attempting to change the books, theories, and especially the minds of all the engineers and scientists around the world would be the cause of mass arguments. It was also assumed that the actual direction didn't really make a real difference, at least as long as everyone stuck to one direction of electrical flow or the other.
Of course, conventional current flow does not work well with vacuum tubes or with the sub-atomic level understanding of magnetism, but it was decided that these problems were less of an issue than trying to change everybody's minds and all the books.
Rather than having engineers and scientists fighting with each other over the direction of current flow, the decision was made that everyone would stay with what has become known as "Conventional Current".
Back to the Present
Nowadays, in general, the electronic technicians use the electron flow
as the direction of electrical current, and the engineers use the conventional direction of electrical current.
Whereas the electronic technician is correct about the movement of electrons, with the exception of electrons traveling through vacuum and the sub-atomic effects of magnetism
, there's really no harm in the scientists' and engineers' concept of the conventional electrical current as electrical flow.
As a matter of fact, for a few scientific purposes, the direction of conventional current helps in understanding. Lightning, for example, starts at the positively charged ground that draws electrons from air molecules close by. As the positive charge travels up, the electrons from further up are drawn down until the whole column of air is ionized, conducting electrons from the negatively charged clouds to the ground.
Liquid or gaseous substances like air, water, even human flesh, have positive ions (atoms without enough electrons to make them neutral) that physically move. These carry their positive charge with them as they travel through the substance. (This flow is really ion migration, but is considered by some to be electrical flow.)
Acid in batteries and electrolytes in electrolytic capacitors are examples of this. Some people consider this to be the correct direction of electrical flow.
However, in electrical design and maintenance, batteries and capacitors are the exceptions and not the rule. They are only components shown on schematics and wiring diagrams.
There is a lot more to the drawings than just these exceptions. For the understanding of electrical current flow in solid materials like copper (lines on the schematics), and components like semiconductors, most capacitors, resistors, inductors and transformers, etc., the atoms stay in place while the electrons move.
Does It Really Make a Difference?
The negatively charged electrons are drawn to the positive terminal of the battery, but don't move more than one atom at a time. While it is perceived that the positive charge on the atoms of the conductor moves to the right, the charge is not moving.
The perceived movement of the positive charge is more like the "Stadium Wave" seen at a football stadium. What looks like an ocean wave is just people standing and sitting. The people aren't moving, they're just standing up and then sitting down again. However, because they are in a synchronous movement, the "Stadium Wave" is perceived to move.
In a wire, the electron leaving a neutral atom takes its neutralizing negative charge with it and leaves the atom positive. The atom just sits there and waits for another electron to balance out the charges again. The question is, "Does that mean nothing is moving to the right, or does that mean that something is moving to the right?"
The answer to that is probably "It Depends".
Getting back to the diagram though, one has to really understand what is being looked at. Is it the negatively charged electron movement to the left, or is it the passing of positive electrical charge to the right, that is the direction of electrical flow?
The answer to this is more about what else is being considered. There are two components to electromagnetic force, for example.
-- Because the individual electrons are moving to the left so slowly and the positive charges are being passed on to the right so fast, the electrical flow would be considered to be electrical charges being passed to the right.
-- Then again, because the positive charges aren't physically moving, and magnetism is tied in with electron or proton movement (in a wire, it's the electron movement that is creating the magnetism), the electrical flow would be considered to be electrons moving to the left.
Standing back and looking at a wire, though, there are three speeds of travel.
-- The positive charges in an atom (positive ions using the "Stadium Wave") do not move at all. The protons are moving at 0.0 meters per second.
-- The individual electrons are moving slowly. An individual electron can take seconds to hours to go from one end of a wire to the other. The electrons are moving at a rate from 1.0 meters per second (or faster) to 0.001 meters per second (or slower).
-- Regardless of which way electrons are moving, or which way the positive ions appear to move, power is traveling either direction on a wire at somewhere around 2/3 the speed of light. Power transfer on a wire, in either direction, is around 200,000,000 meters a second.
Movement of Power
In a wire, the positive ions just look like they're moving in one direction, the electrons are slowly moving in the other direction, and power zips very fast in either direction.
-- In order to use Ohms Law (E = I x R)
or Watts Law (P = I x E)
, electrical current (I)
has to be quantified. The agreed on quantity is tied to the number of electrical charges going past a specific point in a wire. (Positive charges for the engineers concerned with designing electrical circuits, negative charges for the technicians trying to deal with the effects of current in a circuit.)
In reality, the "Statium Wave" movement of positive charges doesn't quite describe electrical flow because, in an electronic circuit, the protons don't move along a wire. Electron movement doesn't quite describe electrical flow because, in the long run, the electrons move so slow. As it moves from one atom to another, each electron jumps quickly, but overall, because the electron keeps stopping on individual atoms, an individual electron is going slowly from one end of a wire to the other.
The Stadium Wave mentioned above is actually part of "Wave Theory", where the electrical current moving in either direction from the battery terminals really isn't the important part, it's the energy being transferred from the power source to the load that's the important part. This transfer involves more than just electrical force and magnetism directly, but capacitance, inductance, propagation, impedance, reactance, frequency, and power.
In electrical theory and electronic theroy, this power transfer is usually done using transmission lines or wave guides, or even propagating at full light speed from transmitting to receiving antennas.
This gets really deep into physics, and the details are still being argued about. I'll have to get into wave theory in another article.
Which direction does electricity flow? The answer to that seems to be just an arbitrary decision, based more on what the electricity is being used for, and based less on the sub-atomic physical characteristics of atoms (the electrons or protons).
Of course, because it's the engineers thinking in terms conventional current flow that are the ones getting to make the electronic symbols we see on schematics, the arrows point in the direction of conventional current flow and not in the direction of electron flow.
The electronic technicians understand this and live with these symbols.
Having serviced fire alarm systems for nearly 20, Douglas Krantz has compiled his knowledge of the causes of Ground Faults and how to reliably detect them into the book Make It Work - Hunting Ground Faults
. The book shows the three types of ground fault, what equipment should be used with each type of ground fault, and how to locate those hard-to-find ground faults.
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