8
What is electricity? Nobody really knows. We only know how
to produce it, understand its properties, and how to control it.
Electricity is the movement of sub-atomic charged particles (called
electrons
) through a material due to electrical pressure across the
material, such as from a battery.
Power sources, such as batteries, push electricity through a circuit,
like a pump pushes water through pipes. Wires carry electricity,
like pipes carry water. Devices like LEDs, motors, and speakers
use the energy in electricity to do things. Switches and transistors
control the flow of electricity like valves and faucets control water.
Resistors limit the flow of electricity.
The electrical pressure exerted by a battery or other power source
is called
voltage
and is measured in
volts
(V). Notice the “
+
” and
“–” signs on the battery; these indicate which direction the battery
will “pump” the electricity.
The
electric current
is a measure of how fast electricity is flowing
in a wire, just as the water current describes how fast water is
flowing in a pipe. It is expressed in
amperes
(A) or
milliamps
(mA, 1/1000 of an ampere).
The “
power
” of electricity is a measure of how fast energy is
moving through a wire. It is a combination of the voltage and
current (Power = Voltage x Current). It is expressed in
watts
(W).
The
resistance
of a component or circuit represents how much
it resists the electrical pressure (voltage) and limits the flow of
electric current. The relationship is Voltage = Current x Resistance.
When the resistance increases, less current flows. Resistance is
measured in
ohms
(
Ω
), or
kilo ohms
(k
Ω
, 1000 ohms).
Nearly all of the electricity used in our world is produced at
enormous generators driven by steam or water pressure. Wires
are used to efficiently transport this energy to homes and
businesses where it is used. Motors convert the electricity back
into mechanical form to drive machinery and appliances. The most
important aspect of electricity in our society is that it allows energy
to be easily transported over distances.
Note that “distances” includes not just large distances but also
tiny distances. Try to imagine a plumbing structure of the same
complexity as the circuitry inside a portable radio - it would have to
be large because we can’t make water pipes so small. Electricity
allows complex designs to be made very small.
There are two ways of arranging parts in a circuit, in series or in
parallel. Here are examples:
Placing components in series increases the resistance; highest
value dominates. Placing components in parallel decreases the
resistance; lowest value dominates.
The parts within these series and parallel sub-circuits may be
arranged in different ways without changing what the circuit does.
Large circuits are made of combinations of smaller series and
parallel circuits.
Introduction to Electricity
Series Circuit
Parallel Circuit