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Introduction to Electricity
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
(
W
), or
kilo ohms
(k
W
, 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.
Series Circuit
Parallel Circuit
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