
I would like to know how does it work the
conductivity of electricity in metals and which
are the units that scientists use in this process.
I would also like to know the several ways for
determining electrical conductivity of metals.
Thank you. 
Question Date: 20130819   Answer 1:
Metals conduct electricity better than any
other kind of material. The reason electrons flow
so easily in metals is because most of them are
free. That is to say, the electrons don't feel
bound to their original host, and can float around
an ocean of metal atoms. In a typical metal,
there's about one electron per atom that is free
to move about. Without an electric field or
electric force applied to the metal, these free
electrons move around randomly and there the
current is in no particular direction. Once an
electrical force is applied, the electrons will
move in the opposite direction the force is
applied.
Electrical conductivity refers to how easily
electrons can move around in a material. The units
of electrical conductivity are Siemens per meter
(a Siemen is just an inverse ohm, which is the
unit for electrical resistance). In my line
of work I measure electrical conductivity in units
of Siemens per centimeter, but it's the same
difference, inverse resistance per unit distance.
You can measure the electrical conductivity by
measuring the electrical resistance. Take whatever
material you want to study and hook it up to a
voltage source, like a battery. Measure the
current flowing through your sample as a function
of voltage using an ammeter. Ohm's law states that
the resistance is proportional to voltage and
inversely proportional to current
R = V/I
(with resistance R, voltage V, and current I).
What you'll likely find after plotting your
data is that the current scales linearly with
voltage, so the inverse slope of your line gives
you your material's resistance. With resistance in
hand, you can calculate resistivity. Resistivity
is equal to the resistance multiplied by the
crosssectional area of the sample and divided by
its length (resistivity = R*A/l with resistance R,
crosssectional area A, and length l).
Conductivity is simply the inverse of the
resistivity (conductivity = 1/resistivity).
That's the essence of how the conductivity of
pure metals is measured. Electrical contacts are
connected between the metal and an electrical
power source and multimeter, and the resistance is
calculated by measuring the current as a function
of voltage. The resistance is then used with the
dimensions of the sample to calculate resistivity
and conductivity.
Keep questioning,
  Answer 2:
Conductivity σ is generally measured in
units of Siemens per meter (S/m). Siemens is a
measure of conductance G, and is the mathematical
reciprocal of resistance (units of Ohm,Ω).
Rarely, Siemens can also be called “mho” (the
lettering inverse of “ohm”). Macroscopic
measurements of objects like metals can be fairly
straightforward. One can connect a voltage or
potential difference (units of Volt, V) across a
piece of, say, metal wire, and measure the
resulting current (units of Amp, A). Using Ohm’s
Law, IR = V, where I is the current and V is the
voltage, we can calculate the resistance R. Then,
taking the reciprocal of this value gives us the
conductance G. If we know the length x of the
wire, we can divide the conductance by this length
G/x to obtain the desired conductivity in Siemens
per meter. Alternatively, one can apply an
electric field E (units of Volts per meter, V/m)
and measure the resulting current I. Then, if we
know the crosssection area A of the wire, we can
once again derive conductivity using the equation
σ = I/AE.
  Answer 3:
Electrical conductivity works by having
electrons that are free to move around in the
material. When a voltage is applied, the
negatively charged electrons will tend to drift
towards the positive field. Scientists measure the
electrical conductivity in units of siemens per
metre (S/m). However, what scientists actually
measure is the electrical resistivity, which is
the opposite. (Something that is more conductive
is less resistive.) The units for electrical
resistivity are ohm metres (Ohm.m). The way that
we measure the electrical resistivity is by
applying a potential to two probes, and then
measuring the electrical resistance between those
probes. For example, when you have a car battery.
These probes can be anything that conducts
electricity, so you could just have a couple
pieces of copper wire, a power source, and an
ohmmeter, which is a device to measure the
resistance.
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