Electronics > Beginners
About electrical impedance and resistance!
Ghitza:
Hello guys,
since this is my first post here I salute you all!
First of all please accept my apologies for my bad english.
I'm an ultra biginer in electronics and surelly there are a lot of unclkear things for me.
As the title say, I am a little confused about the resistance and the impedance.
As you can see this:
"Electrical impedance, or simply impedance, describes a measure of opposition to alternating
current (AC). Electrical impedance extends the concept of resistance to AC circuits, describing
not only the relative amplitudes of the voltage and current, but also the relative phases. When the
circuit is driven with direct current (DC) there is no distinction between impedance and
resistance; the latter can be thought of as impedance with zero phase angle."
I understood about impedance that is specific to an alternating signal but, where it say upper there is no distinction
between those two in DC, is it OK for me to say "impedance" instead "resistance" when I do a measurement in a circuit?
The complete article is here: http://bmia.bmt.tue.nl/people/BRomeny/Courses/8C120/pdf/ElectricalImpedance.pdf
And to expres myself clearly I have made a measurement with a Philips PM2403 on an arduino board.
With the multimeter seted on x10Ω I receive a resistance value of about 570Ω.
I know the measurement it is made in DC but can I also say there is an impedance of 570Ω instead of resistance?
Thank you very much guys!
The Soulman:
--- Quote from: Ghitza on February 05, 2019, 08:10:58 pm ---I know the measurement it is made in DC but can I also say there is an impedance of 570Ω instead of resistance?
Thank you very much guys!
--- End quote ---
No, when measuring with dc you only know resistance.
Impedance is always related to frequency, and therefore that frequency should also be stated, i.e. 100 Ohm at 100Hz.
Or more common: a nominal or average impedance across a certain frequency range.
IanB:
Impedance has two components, resistance and reactance. When energized with AC both resistance and reactance are present and impedance is the result. When energized with DC the reactance component disappears and only resistance remains. Under these circumstances impedance is identical to resistance.
The Soulman:
Attached is a plot for a small woofer (loudspeaker), it is advertised as 4 Ohm "nominal" dc resistance is actually 3,4 Ohm.
Ghitza:
--- Quote from: IanB on February 05, 2019, 08:50:07 pm ---Impedance has two components, resistance and reactance. When energized with AC both resistance and reactance are present and impedance is the result. When energized with DC the reactance component disappears and only resistance remains. Under these circumstances impedance is identical to resistance.
--- End quote ---
Thank you very much Sir for the explanation.
So in my case with the multimeter can I say there is an 570 ohms impedance
or it is mandatory to use the resistance term every time?
Kind Regards!
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