I have been convinced that "impedance" is the ratio of force to response
in any media. That has worked well for me. Maybe there are readers who can
set me straight if I've been wrong.

Jerry



"Peter O. Brackett" wrote in message
news
Richard:

Hmmm....

Impedance... let's give it its' proper due!

It was the self taught "electrician", and ultimately Fellow of the Royal
Society, Oliver Heaviside, FRS
[1850 - 1925] who was born in the London slums to a very poor family and
who
had never attended
any school beyond the age of 16 who was the person who coined, defined and
first used the terms
"impedance", "admittance", and "reactance".

Oliver Heaviside also gave us Maxwell's Equations in the form we now know
them. Maxwell
wrote his equations in the form of 22 separate equations using the arcane
method of "quaternions".
Heaviside simplified those 22 equations given by Maxwell down to the four
simple equations with
two auxilliary constituent relations that we now know and love.

James Clerk Maxwell was a Cambridge educated mathematician from an
affluent
and educated family.
Oliver Heaviside was a poor kid from the London slums who had to go out to
work at age 16 and
never saw the inside of a college or university!

Heaviside never appeared to receive the citation at the ceremony to which
he
was invited when he
was inducted as a Fellow of the Royal Society after he was duly elected to
that lofty title by the
greatest Scientists of the day.

"Impedance"... thank you Oliver!

--
Peter K1PO
Indialantic By-the-Sea, FL


"Richard Harrison" wrote in message
...
Steve Nosko wrote:
"Apparently, because of the way the big bang occurred, when we put a
voltage across a resistor current flows in a manner that we discovered
follows the equation called Ohm`s law."

Big bang? Ohm wasn`t around then. He lived 1787 to 1854. Ohm discovered
that current in an electrical resistance is proportional to voltage.

Resistance is the type of impedance (opposition to electrical current)
in which current is locked in step to the applied voltage.

The item called a resistor is the type of resistance that converts
electrical energy to heat energy.

Not all resistances are resistors. Some resistances don`t convert
electrical energy directly into heat. In these non-dissipative
resistances, current drop is in-phase with the applied volts, or voltage
dropped across the resistance is in-phase with current through the
resistance, but it does not cause energy loss. An example of lossless
resistance is the Zo or surge impedance of a transmission line. Zo is
caused by the distributed inductance and capacitance of the line, but
current in the line is in-phase with the voltage across the line. Zo is
the voltage to current ratio of the waves traveling in either direction
on the transmission line. Zo = volts/amps, yet converts no energy to
heat in the lossless line. Another example of lossless resistance is
"radiation resistance". This is the desired antenna load, so it is
hardly a loss. Loss in the wire, earth, and insulators of the antenna
are resistive loads which produce heat but don`t help the signal.

An ohm is the unit of resistance. It is defined at 0-degrees C, of a
uniform column of mercury 106.300 cm long and weighing 14.451 grams. One
ohm is the resistance which drops one voltt when a current of one amp is
passed through it.

Reactances are also defined by their volts to amps ratios (ohms). The
big difference is that reactance does no work and produces no heat.
Opposition to electrical current comes from delay required to store ard
retrieve energy to and from fields in and around the reactances. Current
lags the applied voltage in an inductance. At time = 0, no current flows
into an inductance, but rises exponentially from the instant of initial
energization. Current leads the applied voltage into a capacitance. At
time = 0, full current flows into a capacitance but voltage across the
capacitance is zero and rises exponentially from the instant of initial
energization.

In an a-c circuit, the current through an inductance lags the voltage by
90-degrees. In a a-c circuit, the current through a capacitance leads
the voltage by 90-degrees. Phase shifts are produced by energy storage
in reactance. There is no phase shift in a resistance. No electrical
energy is stored in a resistor, but its matter does have a thermal
capacity. Once its atoms are agitated by heat their inertia is evident
in the resistance`s temperature. It takes time to cool.

Steve wrote: "Things get all messed up."

As old Carson Robinson sang: "Life gets tedious, Don`t it?" Steve gave
the formulas for capacitive and inductive reactances. They have always
seemed convenient to me. Steve says: "---we call this new kind of
(corrupted) resistance "Impedance"."

No. Impedance is the general name for opposition to electricity.
Resistance is the specialized name for the case in which the impedance
alone causes no delay and stores no electrical energy. All electrical
impedance is defined by its voltage to current ratio, and is the total
opposition (resistance and reactance) a circuit offers to the flow of
electricity. For d-c, reactance doesn`t count. For a-c, total opposition
consists of the vector (phasor) sum of resistance and reactance in a
circuit. Impedance is measured in ohms and its reciprocal is called
admittance. The symbol for impedance is Z. The symbol for admittance is
Y.

Steve also writes:
"Poof! BUT converts it into radio frequency energy (RF) also called an
electromagnetic field or wave."

Yes. A radio wave is r-f energy which has escaped the confines of wires
and doesn`t come back. Whenever wires in open space carry high-frequency
current, some energy gets away as a radiated field, having a strength
that varies inversely with the distance.

Best regards, Richard Harrison, KB5WZI