CONDUCTORS
-
These are materials
in which it is easy
to get electrons to
move and provide a
flow of electric
current.
-
Conductors are
mostly metals such
as gold, silver,
copper, iron and
lead.
-
Carbon is a
conductor as well as
some gases (as in
fluorescent tubes)
and water containing
some chemicals.
-
These are not
perfect conductors
and offer some
resistance to the
flow of current.
The resistance of a
conductor (such as a
metal rod) is determined
by three things.
(1) its length. The
longer its length the
higher its resistance.
(2) its cross-sectional
area. The bigger this is
the lower is its
resistance.
(3) the material of
which it is made.
All materials have
RESISTIVITY. The higher
the value of resistivity
the higher the
resistance.
It is measured in OHM
METERS.
length x resistivity
Resistance =
-------------------------------
cross-sectional area
INSULATORS
-
These are materials
in which it is
difficult to get
current to flow.
Examples are rubber,
pvc, paper,
polystyrene and
oil.Even with these
it is possible to
get some current
flowing if the
applied voltage is
high enough.
-
There is another
class of materials
called
semi-conductors.
These have a
resistance between
insulators and
conductors.
Examples are silicon
and germanium and
are used in diodes
and transistors.
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