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 Charge • Amps • Volts Ohms



Charge is a fundamental physical property of some sub-atomic particles.  It comes in two polarities:  negative and positive.  Each charge is surrounded by an electromagnetic field that attracts opposite charge and repels same-signed charge.

The electron has a full dose of negative charge and the proton has a full dose of positive charge.

Electrons are tiny, fast-moving, and abundant particles that tend to surround more massive, positively charged nuclei.  One nucleus and its cloud of electrons is called an atom.

Atoms, themselves, bond electromagnetically with other atoms to form even more stable electrical 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 is equal to the combined charge of about 6.24 quintillion (1018 or a billion billion) electrons.




Some atoms have weakly bound, unpaired electrons on their outer fringes that can flow en masse in materials called conductors.  Metals like tin, copper, and gold have lots of free electrons and are good conductors.

The flow of charged particles is called electric current.  The standard unit of current is the ampere (or amp for short) and is abbreviated "A" (capital A because Ampère was a person).  One ampere is the flow of one coulomb per second.

Materials whose electrons are all tightly bound are called insulators.  These materials, like wood, rubber and glass, are poor conductors of electric current.




Resistors are engineered from materials like carbon that fall in between conductors and insulators.  They obstruct current in a partial, controllable way.

Resistors have no pool of free electrons that can be shoved downstream domino-style.  Some electrons drift through the atomic lattice but mostly they're captured, yielding more heat than current.

A pressure (potential difference) called a voltage rises across a resistor like water pressure rises across a clogged drain.  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 carrying one ampere of current and losing one watt of power.




If we divide the voltage across a resistor by the current through it (volts/amps), we get a number that's constant for that resistor.  So if we double the voltage, the amperage also doubles.

This constant is called the resistance of the resistor.  The standard unit of measure is the ohm, abbreviated "Ω" (capital Omega because Ohm was a person).

The math symbols for voltage, current, and resistance are "V", "I", and "R" and the equation R = V/I is called Ohm's Law even though it was discovered a century before Ohm popularized it.


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