Is electrical energy transmitted by the actual flowing of electrons, like mechanical energy being transmitted by water flowing in a pipe? Or does it
move along the medium without the medium flowing, like a water hammer or wave?ScienceSquirrel - 26-9-2008 at 08:32
It does. Electricity, in general, is due to the motion of charges; in wires, these happen to be unbound electrons, but in solution ions of both
polarity carry charge. This is exactly analogous to water flowing in a pipe, where mass flow results in mechanical work instead of electrical flow
resulting in electrical work.
Realize that the actual flow rate may be quite small, because the number of electrons is relatively high (wheras 1 l/min of water carries 5.56 x 10^23
molecules per second at a number density of 3.33 x 10^28 n/m^3, 1A of current carries only 6.25 x 10^18 electrons per second at a density (in copper)
of 8.46 x 10^28 n/m^3, so although the number densities are similar, electric currents carry more energy. The implication is that, if you put some
electrons in one end of a wire (as if you could tell them apart, which you can't), you won't get them back out for a long, long time. This is like
putting a small current through a large water pipe, the flow just isn't very high. When that current is applied, however, it appears almost
instantaneously at the other end, because it creates a pressure wave that carries along the wire and starts flow at the speed of sound
(electromagnetic "pressure" waves travel at roughly the speed of light). So the actual speed isn't at all very important, except to certain physics
experiments.
Alternating current takes that idea to its conclusion (with some other important consequences due to magnetism), and on average, the electrons go
exactly nowhere! This is why Dave Barry can say power companies haven't sold any new electricity since 1937. http://www.jimpoz.com/jokes/electricity.html
Timwatson.fawkes - 26-9-2008 at 09:45
Electricity flows through charge carriers. Most often these carriers are electrons, such as in metals (say, in the form of wire). Sometimes they are
not. In electrochemistry, it's typical for the charge carriers to be ions. It's also possible to have multiple simultaneous species of charge
carriers, going in one or both directions.franklyn - 26-9-2008 at 11:32
It is useful to think of electrons as a gas drifting through a porous medium ( the conductor ).
Mathematically it is a " random walk " the current is just the bias produced by the
electromotive force. For direct current this drift usually amounts to a tenth of an inch per
second. Energy is entirely in both the magnetic field ( resulting from the electron drift ) and
the electric field ( which is the gradient between + / - measured as voltage , it was even
referrred to as pressure early on ). Very high frequency alternating current is just waves of
energy without appreciable electron displacement.
The practice now is to express all things electrical in the " conventional current " standard.
This describes the current as positive charged virtual particles moving in the reverse direction
to the electrons. Think of this as the absense of an electron. In fact in semiconductors it
is descriptively called a " hole ". Ths illustrates that the energy in a circuit is a property
of the circuit distinct from a physical particle.
This is over my head but I appreciate it's significance.
This is Nobel prize class work.
A somewhat simplistic and tautological explanation :
When you flip a coin you do not know what the result will be , except it can be either a head or a tail.
When you know what the result will be , because you have chosen the result you want , you do not know when
you will flip this desired result. It may be the first or ten or more later.
• If you know when you flip ( you flip now ) then you don't know what the result will be.
• If you know the result , then you do not know when you will flip it.
.IrC - 19-12-2014 at 18:31
I like the way William J. Beaty explains things in a way beginners can easily grasp various concepts, such as electrons in a DC circuit flowing slower
than Molasses.
I used to think a measurement didn't exist until it was real. Now it seems reality doesn't exist until it is
measured.
Makes sense since a signal doesn't exist until it is sent , so logically one can't send a signal until it is made.
