J
John Larkin
- Jan 1, 1970
- 0
Setting the imaginary term to zero leaves only resistance which is what I
stated can only be observed in DC circuits.
This is merely a semantic argument
John,
Looks like your second post and my third post almost crossed in the system
and say essentially the same thing expressed two different ways.
Setting the imaginary term to zero leaves only resistance which is what I
stated can only be observed in DC circuits.
Setting the imaginary term to zero leaves only resistance which is what I
stated can only be observed in DC circuits.
Dorian said:Setting the imaginary term to zero leaves only resistance which is what I
stated can only be observed in DC circuits. This is merely a semantic
argument so I'll leave you with the Wikipedia definition for impedance (not
my first choice but readily available):
"Electrical impedance, (sometimes Electric impedance) or simply impedance,
is a measure of opposition to a sinusoidal electric current. The concept of
electrical impedance generalizes Ohm's law to AC circuit analysis. Unlike
electrical resistance, the impedance of an electric circuit can be a complex
number. Oliver Heaviside coined the term impedance in July of 1886"
Uriah said:I seem to be real slow in grasping these simple concepts. Another
question on Impedance.
What is low impedance? and what does it mean? Can you have low
impedance with high voltage or does it only apply to current? Is it
just a relative thing. When dealing with digital circuits does
low/high impedance imply certain things? What things?
thanks again
Dorian said:Setting the imaginary term to zero leaves only resistance which is
what I stated can only be observed in DC circuits.
This is merely a
semantic argument
so I'll leave you with the Wikipedia definition for
impedance (not my first choice but readily available):
"Electrical impedance, (sometimes Electric impedance) or simply
impedance, is a measure of opposition to a sinusoidal electric
current.
The concept of electrical impedance generalizes Ohm's law to
AC circuit analysis.
Yes.
Unlike electrical resistance, the impedance of
an electric circuit can be a complex number. Oliver Heaviside coined
the term impedance in July of 1886"
Resistance is not a DC effect. It is an instantaneous effect. Ohm's
law is an instantaneous law, not a DC one. Infinite duration is not
required for it to be a valid description of resistance.
10 ohms resistance means that the instantaneous ratio of the
instantaneous voltage across the resistance is 10 times the
instantaneous current through it, regardless of the duration or speed
of variation or either voltage or current.
Besides DC is a sinusoidal frequency. It just happens to be a
frequency of zero.
Impedance generalized the (frequency independent) concept of
resistance to include reactance, which is frequency dependent and does
not have a fixed instantaneous ratio of voltage to current throughout
an AC cycle. This requires replacing the instantaneous ratio of
voltage to current with a two dimensional value, related to frequency.
One way to describe impedance is to call the magnitude of the
impedance the ratio of the RMS single frequency voltage across the
pair of nodes divided by the RMS single frequency current through the
nodes and add a term that describes the phase shift between voltage
and current. This is the polar form of impedance. Note the two
dimensions required (magnitude and phase). There is also a Cartesian
form that keeps track of the two dimensions as a real and imaginary
part, with the imaginary part being the frequency dependent part.
Silly me, I keep sending them money!
Rich said:Where the heck were you when they were trying to teach me this stuff? ;-)
Gosh, that's not what they taught me in engineering school. They
claimed that impedance is the vector sum of resistance and reactance.
Thanks for straightening me out. I'll ask for my money back.
DC resistance is resistance, not impedance. AC has impedance.
Dorian said:Setting the imaginary term to zero leaves only resistance which is what I
stated can only be observed in DC circuits.