Electric Current: Random or Flow
In physics class, we were told that electrons
physically move in the wire with a direct current applied to that
wire. My dad says that there is random movement; however, energy
is transferred from atom to atom by increasing the energy to the
adjacent atom. Which view is correct or are they both the same?
First, you do not apply a current to a wire. A voltage is applied to a
wire. The average effect is a direct current. Of course, the motion of the
electrons as they pass from atom to atom is really quite random. However,
there is more motion in one direction than in the other. This is why we can
say the current is in only one direction.
The voltage on the wire is due to a device (usually a battery) that makes
the electron energy at one end of the wire greater than energy at the other
end. The energy is stored in an electric field.
As the electron moves "forward" along the wire, the electric field gives
energy to the electron. Also, electrons lose energy when they collide with
atoms. This is what makes the wire warm. Electrons moving backward lose
energy to the wire. Electrons moving backward gain energy from the electric
field and lose energy to the wire. The forward electrons move a little
faster. Electrons that enter the battery are moved through by chemical
means and then emitted at the other end. The net effect is an average
forward drift at the speed comparable to that of a snail.
Each metal atom in a wire donates one electron to the current. When you
consider the number of atoms in a wire, we can see how large currents exist.
The size of a current depends on the number of electrons traveling through
the wire just as much as it depends on the average drift speed of the
Dr. Ken Mellendorf
Illinois Central College
The 'movement' of electricity and the movement of individual
electrons are two distinct, yet related occurrences. I find it best
to use an analogy in this case.
Instead of thinking of the wire as so many distinct atoms, think of
the wire as a large cardboard tube filled with marbles. (the marbles
here represent electrons, which move more or less freely about the
different atoms of a good conductor.)
Now, by shoving one more marble into one end of the tube, another
marble will be forced out the other end. Although you are not
pushing your new marble in at any great speed, the effect is
practically instantaneous at the other end.
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Update: June 2012