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In electricity, current refers to electric current,
which is the flow of electrons. Lightning is an example of an electric current, as is the solar wind, the source of
the polar aurora.
Probably the most familiar form of electric current is the flow of conduction
electrons in a metallic
wire. This is how utility companies deliver electricity. In electronics, electric
current is most often the flow of electrons through conductors
and devices such as resistors,
but it is also the flow of ions
inside a battery or the flow of holes
within a semiconductor.
Conventional current was defined
early in the history of electrical science as a flow of positive charge. In
solid metals, like wires, the positive charges are immobile, and only the
negatively charged electrons
flow in the direction opposite conventional current, but this is not the case
in most non-metallic conductors. In other materials, charged particles flow in
both directions at the same time. Electric currents in electrolytes are flows
of electrically charged atoms (ions),
which exist in both positive and negative varieties. For example, an electrochemical
cell may be constructed with salt water (a solution of sodium
chloride) on one side of a membrane and pure water on the other. The
membrane lets the positive sodium ions pass, but not the negative chlorine
ions, so a net current results. Electric currents in plasma
are flows of electrons as well as positive and negative ions. In ice and in
certain solid electrolytes, flowing protons constitute the electric current. To simplify this
situation, the original definition of conventional current still stands.
are also instances where the electrons are the charge that is physically
moving, but where it makes more sense to think of the current as the movement
of positive "holes"
(the spots that should have an electron to make the conductor neutral). This is
the case in a p-type semiconductor.The
SI unit of electrical current is the ampere.
current is therefore sometimes informally referred to as amperage or ampage, by analogy with the term voltage. Though this
is a valid term, some engineers frown on it.