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    Charge - Current - Resistance - Voltage

CHARGE

Charge is a fundamental property of some sub-atomic particles of matter.  For example, electrons have one dose of negative charge, protons one dose of positive charge.  Opposite charges electromagnetically attract while same-signed charges repel.

Electrons are tiny, fast-moving and abundant.  Electromagnetic attraction causes them to gather around more massive, proton-laden nucleuses.  One nucleus and its cloud of electrons is called an "atom".

Atoms, in turn, bond electromagnetically to other atoms, forming even more stable electrical landscapes or "fields".  Tennis balls bounce, buildings stand, and aspirin thins the blood thanks to electromagnetic fields.

CONDUCTORS, CURRENT, and INSULATORS

Unpaired electrons on the outer fringes of atoms are weakly bound to their nuclei and can flow en masse in materials called "conductors".  Metals like tin, copper, and gold have lots of free electrons and are good conductors.

A flow of charged particles is called an electric "current".  The unit of measure for current is the "ampere" (or "amp" for short), abbreviated "A" (capital A because Ampère was a person).

Materials having tightly bound electrons are called "insulators".  These materials, like wood, rubber and glass, are poor conductors of electric current.  They're like dams or steep shorelines to the flow of current.

RESISTORS and VOLTAGE

"Resistors" are engineered from materials like carbon.  They impede electric current in a partial, controllable way.  These materials have no pool of free electrons that can be shoved downstream domino-style.  Some electrons will drift through the atomic lattice but most are stopped by it, producing more heat than electric current.

Electrical pressure rises across a resistor like water pressure rises across a clogged drain.  The pressure difference between one end of the resistor and the other is called the "voltage" across the resistor.  The unit of measure for voltage is the "volt", abbreviated "V" (capital V because Volta was a person).

OHM'S LAW

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.  In other words, if we double the voltage across it, the current through it will also double.

This constant is called the "resistance" of the resistor.  Its 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".  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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