wires behaviour

Discussion in 'General Electronics Chat' started by ritu singh thakur, Jan 4, 2015.

  1. ritu singh thakur

    Thread Starter New Member

    Jan 4, 2015
    what it mean wire could be treated as ideal equipotential nodes with lumped capacitance
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    Firstly look at this, it explains how wires are considered as ideal conductors where the potential along the wire does not vary.

    This is also true for for wires that are short compared to the wvelength of an alternating signal.


    Now there is a capacitance between two points at different potentials.
    So there is a capacitance between two circuit nodes.
    This capacitance may or may not be significant.
    The signifcance depends upon the nature of the signal, since it will be frequency dependent.
    The signifcance is also likely to be increased by physical closeness of the wires or nodes.

    The significance is that it can introduce unwanted paths for the signal.
    These can be feedback paths or loss paths to earth or 'cross coupling' (where a signal in one part of a circuit get into another where it is not wanted).

    For short wires these unwanted paths can be modelled in circuits as single capacitors connecting the nodes concerned.
    These single capacitors are therefore examples of additional (unwanted) lumped components in the circuit.

    Miller capacitance is a good example of this.


    This is quite distinct and different from distributed capacitance you find in transmission lines, where the wires are long compared to the signal wavelength.
    (see note 2 at the bottom of my first link)

    However your original post was very short and did not tell us much about the source.

    It could be simpler than I have said above.

    It could simply be that your textbook means that physical circuit capacitors can be modelled as circuit elements connected between the nodes.
    Last edited: Jan 4, 2015
    ritu singh thakur likes this.
  3. ritu singh thakur

    Thread Starter New Member

    Jan 4, 2015