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Instructor
Note |
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The
purpose of this target indicator is that students realize
that the networking devices and components with which they
will be working are based on very precise control of
electron flow using a combination of conductors (usually
copper conducting paths), semiconductors (usually
Silicon-based Integrated Circuits), and insulators
(usually plastic or rubber to form plugs, connectors,
cable jackets).
There are
many demonstrations possible with a digital multimeter.
You can show that the electrical resistance of objects
gives us a measure of whether a material is a conductor
(low resistance), semiconductor (moderate resistance), or
insulator (high resistance). You could demonstrate a low
voltage series circuit with a 6 V lantern battery, a low
voltage light bulb, a pencil, some plastic, some alligator
clip leads, and a piece of copper. Make a complete circuit
with the copper piece and the bulb burns brightly. Make a
complete circuit with a short piece of pencil graphite and
the bulb burns dimly. Make a complete circuit with a piece
of plastic and the bulb does not glow. |
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Atoms, or groups of atoms called molecules, can be
referred to as materials. Materials are classified as belonging to one of three groups,
depending on how easily electricity, or free electrons, flows through them.
Electrical Insulators 
Electrical insulators, or
insulators, are materials that allow electrons to flow through them with great difficulty, or not at all.
Examples of electrical
insulators include plastic, glass, air, dry wood, paper, rubber, and
helium gas. These materials have very stable chemical structures, with orbiting electrons tightly bound within the atoms.
Electrical Conductors
Electrical conductors, or conductors, are materials that allow electrons
to flow through them with great ease. They flow easily because the outermost electrons are
bound very loosely to the nucleus, and are easily freed. At room temperature, these
materials have a large number of free electrons that can provide conduction. The
introduction of voltage causes the free electrons to move, causing a current to flow.
The periodic table categorizes some groups of atoms by
listing them in the form of columns. The atoms in each column belong to particular
chemical families. Although they may have different numbers of protons, neutrons, and
electrons, their outermost electrons have similar orbits and behave similarly, when
interacting with other atoms and molecules. The best conductors are metals, such as copper
(Cu), silver (Ag), and gold (Au). All of these metals are located in one column of the
periodic chart, and have electrons that are easily freed, making them excellent materials
for carrying a current.
Other conductors include solder (a mixture of lead (Pb) and
tin (Sn), and water with ions. An ion is an atom that has more electrons, or fewer
electrons, than a neutral atom. The human body is made of approximately 70% water with
ions, which means that it, too, is a conductor.
Electrical Semiconductors
Semiconductors are materials where the amount of electricity they conduct can be precisely controlled. These materials are listed together in one column of the periodic chart.
Examples include carbon (C),
germanium (Ge), and the alloy, gallium arsenide (GaAs). The most
important semiconductor, the one that makes the best microscopic-sized
electronic circuits, is silicon (Si). 
Silicon is very common and can be found in sand, glass,
and many types of rocks. The region around San Jose, California is known as Silicon Valley
because the computer industry, which depends on silicon microchips, started in that area.
Whether materials are classified as insulators, conductors,
or semiconductors, it is the knowledge of how each one controls the flow of electrons, and
of how they work together in various combinations, that is the basis for all electronic
devices.
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