General Electronics
Ohm's Law
By Douglas Krantz
If it isn't just a word, and it isn't really something to be memorized in order to pass a test, what do the letters in Ohm's Law really mean?
The electrons are found in layered clouds around the nucleus of atoms. The protons in the atom don't move from atom to atom, but the electrons can be pushed and pulled from atom to atom using electrical force. The force is called Electromotive Force (EMF). EMF is measured in voltage.
Electron
The letters in
Ohm's Law show
a relationship
between
voltage, current,
and resistance,
and at the
heart of that
relationship
is the electron.
Electomotive Force (EMF), like pressure pushing on water, or like gravity pulling everything on earth, is what pushes and pulls electrons to cause them to jump from one atom to the next. Electromotive Force is measured in Voltage.
Electromotive Force
"E" stands for
Electromotive Force
(EMF).
It's the driving
muscle that
moves the electrons.
Voltage
Measured in Voltage,
EMF pushes and
pulls on the
electrons.
Electrical Current is the number (quantity) of electrons going past a given point in an electrical circuit, like the number of cubic meters of water that goes over a falls in a second. Electrical Current is measured in Amperage, or Amps for short.
Electrical Current
"I" stands for
"Intensité de Courant"
(French), or Current Intensity.
AndréMarie Ampere, who
discovered electrical current,
used this symbol.
Current
Is Electron Movement
Amperage (Amps)
Measured in Amps, and
hopping from one atom
to the next, the organized
movement of electrons
going past a point is
electrical current, or "I".
Resistance is the amount of opposition to electrical current. This can be likened to the diameter of a pipe resisting the flow of drainage from the bathtub. The larger the pipe (lower resistance) the faster gravity can pull the water out of the bathtub.
Resistance
"R" stands for
Resistance. It
restricts, or slows
down, the
movement
of electrons.
Resistance
Counters Electron Flow
Resistance (Ohms)
Measured in Ohms,
resistance opposes
electron flow.
The greater the
resistance, the
less the electrons
flow.
A greater amount of water will flow when the valve is opened wider; more electrons will flow when there is less resistance.
A lessor amount of water will flow when the valve is more closed; less electrons will flow when the resistance is greater.
Resistance
Assuming the electromotive
force remains the same,
reducing the resistance,
like opening a valve on
a water pipe, will increase
the number of electrons
that flow.
The opposite is also true,
increasing the resistance
will reduce the number of
electrons that flow.
Greater water pressure pushes more water through the same pipe; greater electromotive force will push more electrons past the resistance. Lessor water pressure means less water; lessor electromotive force means fewer electrons.
Current Flow  Quantity of Electrons
The quantity of electrons
flowing, electrical current,
is determined by the
electromotive force 
reduced by the resistance.
Similarly, the quantity of
water flowing is determined
by water pressure,
reduced by the restriction
of the pipe.
Does not affect
R
(Resistance)
Does not affect
EMF
(voltage)
Electromotive Force (EMF) and Resistance (R) don't affect, or change, each other.
The greater the EMF (voltage) the greater the current (amperage); the lessor the EMF the lessor the current.
Voltage and Current
The amount of
electromotive force
(voltage) directly
affects current flow.
Current goes up
and down as
EMF goes up
and down.
The greater the resistance (Ohms), the lessor the current (Amps); the lessor the resistance, the greater the current.
Resistance and Current
The amount of
resistance inversely
affects current flow.
As resistance goes
up, current goes
down, and as
resistance goes
down, current
goes up.
Voltage and Resistance don't actually affect each other, Voltage (E) and Resistance (R) both will change the current (I).
Interrelated
The relationships
between the
electromotive force,
current and
resistance are all
interrelated, and
described in a single
formula, or law.
Volts of Electromotive Force
E
=
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