# impedance

Discussion in 'General Electronics Chat' started by veenife, Jan 16, 2014.

1. ### veenife Thread Starter Member

Jan 16, 2014
42
0
hey, cant reaaly get the difference of input and output impedance... whats are them exactly?

2. ### LvW Active Member

Jun 13, 2013
674
100
It`s not too complicated.
Input impedance is the impedance at the input - and output impedance...can you guess?

3. ### JDT Well-Known Member

Feb 12, 2009
658
85
Not sure that answer is really helpful to a beginner (actually reminds me of Microsoft help).

Impedance is the complex resistance - resistance that depends on frequency.

First: what is input and output resistance?

Input resistance is not too difficult to understand - it's the resistance that appears across the input terminals. The amount the input "loads" the thing that is driving it.

Output resistance is a bit more difficult to understand - for instance you can have a tiny little 12V battery: connect a car headlamp across it and the voltage collapses, lamp does not light. Try the same with a well-charged car battery, lamp lights, voltage hardly changes.

The difference is the output resistance of the two batteries. That's all!
The small battery has a high output resistance. Car battery has a low output resistance.

Real sources of power have inductance and capacitance as well. The resistance depends on frequency. The combination of resistance, inductive and capacitive "reactance" is called impedance.

Any help?

Last edited: Jan 16, 2014
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4. ### LvW Active Member

Jun 13, 2013
674
100
I think, it exactly did answer the question.
I know that it was not of great help - on the other hand, somebody who wants to gain some knowledge should learn at first to ask a precise question.
For my opinion, everybody who is expecting that forum members provide some help, should also be able to spend some time for preparing his request.
At least, the OP should mention if he have in mind a battery, an amplifier or any other active or passive system. This is important to find the correct answer.

5. ### Veracohr Well-Known Member

Jan 3, 2011
559
77
Are you familiar with Ohm's law and how voltage drops across, say, two resistors in series? If you are, input and output impedances are like the resistors (although they may be frequency-dependant, so they're called impedance instead of resistance).

6. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
I agree with LvW.

I have seen this sort of provocative trolling happening more and more on other tech forums recently.

I would be very sorry to see it come here where we have a relaxed and welcoming attitude to those with a genuine interest in the subject.

LvW likes this.
7. ### LvW Active Member

Jun 13, 2013
674
100
Some days ago, I have seen another "question" in this forum:
What is the outcome of a short circuit: Low or high current?