Charge is a fundamental property of some sub-atomic particles. It comes in two polarities:
plus and minus.
Each charged particle is surrounded by an electromagnetic field that pulls on
oppositely charged particles but repels similar ones.
The electron, for example, has one elementary negative charge
while the proton has one elementary positive charge.
Electrons are tiny, fast-moving and abundant and tend to
surround more massive, positively charged nuclei. A nucleus and its
cloud of electrons is called an atom.
Atoms, themselves, bond electromagnetically with other atoms to form even more stable
fields. Tennis balls bounce,
buildings stand, and aspirin thins the blood thanks to these fields.
The standard unit of electrical charge is the coulomb, which equals the combined
charge of about 6.24 quintillion (1018 or a billion billion)
CURRENT, CONDUCTORS, INSULATORS
In the periodic table, the transition metals have lots of electrons
that are very loosely bound to their nuclei. These electrons can flow en masse through the atomic lattice. Tin, copper,
nickel and gold are examples of such electrical conductors.
Flowing electrons comprise an electrical current.
The standard unit of current is the ampere, or amp, and is abbreviated "A"
(capital A because Ampère was a person). One amp equals the
flow of one coulomb of charge per second.
Other materials, like wood, rubber and glass are filled with electrons
that are tightly bound to their nuclei and unable to flow freely.
These materials are called
RESISTORS and VOLTAGE
A resistor is an electronic component that's engineered from materials like carbon,
which fall between a conductor and an insulator. Resistors block electrons
to a extent that
can be controlled during manufacture.
In a resistor, there's no pool
of free electrons to force downstream domino style. Some
electrons will drift through the atomic lattice but many are stopped by it,
yielding more heat than electrical current.
Like a clog in a drain, a pressure builds up across the resistor. This
electrical pressure, or potential difference, is called a voltage.
The standard unit of voltage is the volt, abbreviated "V" (capital V
because Volta was a person).
One volt is the potential difference between two points of a circuit
that carries one amp of current but loses one watt of power.
When you measure the voltage across a particular resistor, and divide
that by the
current flowing through it, the result is always the same for that
resistor. In other words, if you double the voltage, the current
will also double. This constant (volts/amps)
is called the resistor's resistance.
The standard unit of resistance is the ohm, abbreviated "Ω" (capital
Omega because Ohm was a person).
The mathematical symbols for resistance, voltage, and current are "
R = V/I is called Ohm's Law even
though the law was
discovered a century before Mr. Ohm popularized it.