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 Charge • Amps • Volts Ohms



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) electrons.




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 electrical insulators.




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 an 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", and "I".

The equation  R = V/I  is called Ohm's Law even though the law was discovered a century before Mr. Ohm popularized it.


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