electrons then travel to the opposite, or
positive, terminal through an EXTERNAL circuit. The electrons
do not travel through the battery itself. Remember that the
flow of electricity is really the flow of electrons. Voltage
can also be created in three other ways. The first is by
friction, or static electricity. The second way is by
magnetism, or electric generator. The last way that voltage can
be created is by light, or solar cell. Voltage is related to
the electrical fields emanating from the charges associated
with particles such as protons, electrons, etc. Voltage is
represented by the letter V, and sometimes by the letter E, for
electromotive force. The unit of measurement for voltage is
volt (V). Volt is defined as the amount of work, per unit
charge, needed to separate the charges. Lab Activity Lab
Exercise: Voltage MeasurementThis lab will demonstrate the
ability to measure voltage with the multimeter safely. Web
Links Learn the basics of electricity to achieve energy
conservation http://www.eccj.or.jp/catalog/2000w-he/
memo/mame6.html
Content 3.1 Copper
Media 3.1.3 Resistance and impedance The
materials through which current flows offer varying amounts of
opposition, or resistance to the movement of the electrons. The
materials that offer very little, or no, resistance, are called
conductors. Those materials that do not allow the current to
flow, or severely restrict its flow, are called insulators. The
amount of resistance depends on the chemical composition of the
materials. All materials that conduct electricity have a
measure of resistance to the flow of electrons through them.
These materials also have other effects called capacitance and
inductance associated with the flow of electrons. The three
characteristics comprise impedance, which is similar to and
includes resistance. The term attenuation is important when
learning about networks. Attenuation refers to the resistance
to the flow of electrons and why a signal becomes degraded as
it travels along the conduit. The letter R represents
resistance. The unit of measurement for resistance is the ohm
(). The symbol comes from the Greek letter , omega. 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, usually
just called 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,
resulting in a current 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), because they have electrons
that are easily freed. 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
the number of protons in the nucleus of the atom. The human
body is made of approximately 70% water with ions, which means
that the human body is a conductor. 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 which 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. Lab Activity
Lab Exercise: Resistance MeasurementThis lab will demonstrate
the ability to measure resistance and continuity with the
multimeter. Interactive Media Activity Drag and Drop:
Insulators, Conductors, and Semiconductors When the user has
completed this activity, the student will be able to identify
the resistance and impedance characteristics of different types
of material. Web Links Are resistance and impedance the
same? http://www.sciencenet.org.uk/database/
Physics/ACCircuits/p00396c.html
Content 3.1
Copper Media 3.1.4 Current Electrical
current is the flow of charges created when electrons move. In
electrical circuits, the current is caused by a flow of free
electrons. When voltage, or electrical pressure, is applied and
there is a path for the current, electrons move from the
negative terminal along the path to the positive terminal. The
negative terminal repels the electrons and the positive
terminal attracts the electrons. The letter “I” represents
current. The unit of measurement for current is Ampere (Amp).
Amp is defined as the number of charges per second that pass by
a point along a path. If amperage or current can be thought of
as the amount or volume of electron traffic that is flowing,
then voltage can be thought of as the speed of the electron
traffic. The combination of amperage and voltage equals
wattage. Electrical devices such as light bulbs, motors and
computer power supplies are rated in terms of watts. A watt is
how much power a device consumes or produces. It is the current
or amperage in an electrical circuit that really does the work.
As an example, static electricity has very high voltage, so
much that it can jump a gap of an inch or more. However, it has
very low amperage and as a result can create a shock but not
permanent injury. The starter motor in an automobile operates
at a relatively low 12 volts but requires very high amperage to
generate enough energy to turn over the engine. Lightning has
very high voltage and high amperage and can do severe damage or
injury. Web Links Basics of Electricity
http://www.gelighting.com/eu/institute/
firstlight/module01/01.html
Content 3.1 Copper
Media 3.1.5 Circuits Current flows in
closed loops called circuits. These circuits must be composed
of conducting materials, and must have sources of voltage.
Voltage causes current to flow, while resistance and impedance
oppose it. Current consists of electrons flowing away from
negative terminals and towards positive terminals. Knowing
these facts allows people to control a flow of
current.Electricity will naturally flow to the earth if there
is a path. Current also flows along the path of least
resistance. If a human body provides the path of least
resistance, the current will flow through it. When an electric
appliance has a plug with three prongs, one of the three prongs
serves as the ground, or zero volts. The ground provides a
conducting path for the electrons to flow to the earth because
the resistance traveling through the body would be greater than
the resistance flowing directly to the ground. Ground typically
means the zero volts level, when making electrical
measurements. Voltage is created by the separation of charges,
which means that voltage measurements must be made between two
points. A water analogy helps to explain concepts of
electricity. The higher the water and the greater the pressure,
the more the water will flow. The water current also depends on
the size of the space it must flow through. Similarly, the
higher the voltage and the greater the electrical pressure, the
more current will be produced. The electric current then
encounters resistance that, like the water tap, reduces the