Franklin’s Folly?
The flow of electrical current
It is generally accepted that electrical current flows
from the positive side of the circuit to the negative
side. However, in the “Human Circuit” article we
learned that electrons generally conduct the current.
We also know that opposite charges attract and like
charges repel. So, if electrons provide the charge, and
repel from the negative end, how can the current be
moving from the positive side to the negative side?
Something does not seem to make sense here.
DISCUSSION:
When Ben Franklin started experimenting with electricity, he
assumed that the electrical current must be “positive.” How
did Ben reach this assumption? He hypothesized that there
were two types of charges that could be generated, and the
charges were dependent upon the types of materials he
rubbed together. One type of charge, he surmised was produced from an excess of “electrical fluid,” which he called
positive, and the other type of charge resulted from a deficiency, which he called negative.
Ben’s assumptions were made long before electricity was
correlated with the electron. In fact, electrons had not even
been discovered yet. According to Ben’s assumptions it
seems logical that the excess “fluid” would flow to the area
that is deficient in “fluid.” His assumptions became widely
accepted. Today we talk about electric current as flowing
from positive to negative. However, we now understand that
electrons have a negative charge, and the flow of electrons
is actually in the opposite direction as the flow of electricity.
So let’s stop and think about this for a moment. If something
has a negative charge we know that it must have an excess
of electrons as compared the number of protons, and if it
has a positive charge then that same substance must be
deficient in electrons, again as compared to the number of
protons. Isn’t this exactly opposite of Ben’s assumptions?
Ok, well what
about protons?
Protons have a
positive charge,
exactly opposite
of the electron.
Can
protons
carry electrical
current? The answer is YES they can. This phenomenon has
been observed in particle accelerators. Indeed, after all
these years, we are finally able to observe that electric
charge carried by protons flows in the direction that Ben
Franklin assumed many years ago.
It is also true that current can be carried by both electrons
and protons at the same time (this happens in electrolytes
and semi-conductors). So it may be helpful to think of electric
current this way: It is not electrons or protons per se moving
through a conductor, instead, it is the vibrational energy of an
electron or a proton that is passed from one atom to the next
through the conductor that creates an electrical current.
So, to understand electricity, do these details make any
difference? It turns out that for a basic understanding of how
electricity behaves these details do not matter much. They
don’t really impact how we use it in our daily lives. Most
electric circuits cannot distinguish whether the charge is
associated with electrons or protons. In fact for general
household appliances, the direction of current flow is
insignificant. However for a pure theoretical discussion of
what electricity really is, and how it really works, our understanding of charged particles is important.
So, in looking back to the late 1700s at the beginning of the
human understanding of electricity:
“Was Benjamin Franklin correct or not?”
Fun Fact: Ben Franklin did not actually fly a kite that was
struck by lightning. If he would have, he would most likely have
died. By the best
accounts, what actually happened was
that he flew a kite
during a storm, and
what was produced
was a charge differential between the
clouds and the Leyden
Jar (a primitive battery). This charge is a larger version of static shock produced
by rubbing your feet on the carpet and then touching a
grounded metal object, but much smaller than the charge
generated by lightning. Franklin’s experiments lead to inventions such as the Franklin Bell and lightning rods.
Show What You Know
Show what you know at the Phenomenal Physics Fair. Use one of the topics covered in the previous
Phenomenal Physics or come up with an experiment on your own. Local top projects will receive a
free trip to Physics Day at Lagoon in May and get a chance to compete for great prizes including
scholarships.
Visit: http://www.portageinc.com/Community/physics.aspx
for more information and to register
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