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

  1. veenife

    Thread Starter Member

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

    Active Member

    Jun 13, 2013
    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
    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
    bance likes this.
  4. LvW

    Active Member

    Jun 13, 2013
    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
    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
    I agree with LvW.

    Was this a serious question or was this an insult to members who have spent years studying properly?

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