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Conventional vs Charge Current
Name: Breta H.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2/26/2003
Question:
A student in fifth grade wrote a report talking about
"conventional electricity" In conventional current the electrons flow
one direction and the current flows in the opposite direction. I have
never come across this concept and cannot find a reference to it. Is is
an accurate concept, and if so, where could I find information about it?
Replies:
Breta,
You can find this information in any standard college text regarding
electricity, as well as many high school texts. The source of the
"disagreement" is a misunderstanding among the first researchers of
electricity.
Electricity was known of long before Benjamin Franklin. It was not
understood very well, but it was known of. Scientists knew there were two
kinds of electric charge. They knew there was electric current. Scientists
believed that the opposite charges moved similarly in opposite directions.
They defined one as positive and one as negative. They defined current to
be in the direction of the positive charges. Later, they learned of their
mistake.
Only the negative charges move freely in conductors. Electrons had been
defined as the negative charges. Current had been defined "backwards". It
was too late to redefine all of electrical physics, so the inconvenience
holds to this day. The direction that the electrons move is opposite the
direction that current points. Because of how electricity works, it isn't
much of a problem. Negative charge moving to the left through a wire has
the same effect as positive charge moving to the right. So long as the
total charge in the wire (protons and electrons) remains balanced, no
trouble occurs.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
Breta,
Conventional current theory is an older and well-ingrained way of
considering electrical flow. I have never liked it much because it is the
excited electrons that are actually doing the work as they move through the
conductor. Since science has agreed that electrons carry a negative charge,
I find it convenient to see the issue as charge flow from negative to
positive in the circuit.
Regards,
ProfHoff 586
Yep!! Fifth grader is right. Electricity was known before the electron was
discovered, and without the knowledge of electrons and their charge, it
makes no difference as far as circuits etc. are concerned, which way
electricity flows. Only when electrochemistry was discovered and one could
observe things like the deposition of silver from a solution of silver
nitrate was is evident that Ag(+) + e(-) -----> Ag(0) showed which way
electrons were moving that it became clear that "conventional electricity"
had the current and the electrons moving in opposite directions.
Vince Calder
Electrical current exists any time charged particles move. I have never heard
the specific term "conventional" to describe current in which the particles
are electrons, but it IS they type of current generated in power plants,
carried through power lines, and used in motors and other electrical gadgets
in our society.
Your student is correct in stating that the current flows in the opposite
direction of the electrons; this is because current is defined as the
positive movement of charge, and electrons have a negative charge. So when
electrons move from A to B, A gets more positive charge and B gets less
positive charge, so we say that current is flowing from B to A. There
really is not anything called "current" moving around; the electrons are
moving. But "current" is a valuable term for what is going on. We can talk
about the action of current in a circuit without needing to worry about
exactly what kind of charged particle is actually moving. The same laws of
electronics will apply in any case.
Other particles can be charge carriers, such as ions in liquid solutions
(salt water, for example). If the charge carriers are positively-charged,
say the Na+ ions in salt water, then the current and the charge carriers
will move in the same direction.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
Early on in the study of electricity it was apparent that there were two kinds
of charge, and that at least one of them was moving somehow through metal in
response to an electric field. With no way of knowing which kind of
charge was
moving, and no knowledge that the charge was carried by particles, Andre
Ampere
made a guess (ok, an operational assumption) that the positive charge was
moving.
This is "conventional current". Later we discovered that the negative
charge is
much more mobile, and is carried by electrons, which move as a gas through a
static arrangement of atoms containing the positive charges (protons, of
course).
One way to find information on things like this is to search the web:
Go to www.google.com, type the following (including quotes)
"conventional current"
into the box, and click the "Google Search" button.
Tim Mooney
We have Ben Franklin to thank for this bit of inconvenience. He
studied electricity long before the electron was discovered and
its charge was measured to be what we now call negative. He had
a fifty-fifty chance of guessing right and, as happens half the
time in such cases, was wrong.
So the conventional current flows from a higher potential to a
lower potential as positively charged particles would, but the
actual charge carriers (in most cases), being negatively charged
electrons, move in the opposite direction. I believe most
elementary texts discuss this.
Best, Dick Plano, Professor of Physics emeritus, Rutgers
University
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