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Hari Ramalingam
09-30-2013 11:56 AM

Difference between impedance and resistance

Can some body please cleary explain the difference between Impedance and Resistance,,, i am getting confused...
09-30-2013 02:46 PM
Top #2
Muhammad Owais
09-30-2013 02:46 PM
well buddy the only difference between impedance and resistance is that we use the term Impedance when we are dealing with AC voltages and we use resistance when we are dealing with DC voltages.
In short where ever frequency is involved then the resistance of the circuit will be refferd as Impedance and when there is no frequency involved then it will be called resistance. and frequency is always present in AC voltages. DC has no frequency.
Frequency dependent resistance is called Impedance.
09-30-2013 05:37 PM
Top #3
Roy Kok
09-30-2013 05:37 PM
And to add to that, the change in voltage and current in an AC circuit causes a magnetic component to be added to the resitance, the magnetic component is opposing the change. Hence for AC circuits, the impedance is higher than the resistance you measure in the DC state.
09-30-2013 08:16 PM
Top #4
Hari Ramalingam
09-30-2013 08:16 PM
Thanks guys
09-30-2013 10:22 PM
Top #5
Bill Ellerton
09-30-2013 10:22 PM
Umm.. not all that easy to explain in a few words. Muhammad has done a great job in really capturing the essence. But then of couse if you turn on DC you effectively have the leading edge of a square wave which meets impedance. Same when you turn DC off and end up with the residual effects caused by impedance not by pure resistance.
10-01-2013 12:37 AM
Top #6
Gabriel Baez Cambra
10-01-2013 12:37 AM
The relationship between the voltage applied and the resulting current in a circuit is called impedance. Due to reactive components in circuit, it is a complex number, where the real part of it is called resistance.
Talking about DC, and keeping aligned with Bill´s explanation when you apply a leading edge of square wave or when you turn off the DC: the impedance reveals itself by a delay to the final value determined by a time constant which depends on the value of the impedance, and makes the leading edge of the wave appear "rounded". Had you only resistive components in your circuit, then the pulse would be square, like an instant response to the step.
10-01-2013 05:53 AM
Top #7
Adrian Stefanik
10-01-2013 05:53 AM
Dear Hari,

If you really want to understand the difference between these two I advise to get any book that deals with the subject, like e.g. Electrical Engineering, Electrical Circuits, or even a physics lectures - there you can find everything you need. If you want you can even search through internet and you'll find the answer too.
You should know also that the difference can be found on many levels, basicly - answers are given already in this discussion, but you can dig deeper and deeper. I depends on what level of understanding of the matter you want to touch.

If you really cannot make it clear to yourself then say, what makes you getting confused actually? If you understand the difference between AC and DC and know what are R, L and C, you should see the difference between impedance and resistance.


// Adrian
10-01-2013 08:50 AM
Top #8
Shiv K Dixit
10-01-2013 08:50 AM
Dear Group Members
Greetings of the day

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If you have some other idea, please share.
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