Understanding Conductance in Circuits

Discussion in 'General Electronics Chat' started by paul_alan, Nov 5, 2011.

  1. paul_alan

    Thread Starter Member

    Nov 5, 2011
    I'm a new student studying electronics and I'm not quite understanding some information about conductance. If resistance is added in Parallel, would the conductance increase or decrease? Also, if resistance was added in Series, would that conductance increase or decrease? And the inverse formulas aren't really making sense either. Is finding the conductance across a load as simple as 1/R=G? Like, is the conductance of a 500 Ohm resisitor 0.002, and what would the conductance total be if a second 500 Ohm resistor was added 1) in Series and 2) in Parallel? I appreciate any help I could get with this information.
  2. Adjuster

    Late Member

    Dec 26, 2010
    Resistance R is in ohms (Ω), or volts per amp.

    Conductance G is in siemens (S) (not s, seconds), or amps per volt.

    These things are each others reciprocals: R=1/G, G=1/R.

    Resistors in series add, Rtotal = R1 + R2 + R3... but in parallel Rtotal = 1/(1/R1 + 1/R2 + 1/R3...)

    Similarly conductances in parallel add, Gtotal = G1 + G2 + G3... but in series Gtotal = 1/(1/G1 + 1/G2 + 1/G3...)
  3. paul_alan

    Thread Starter Member

    Nov 5, 2011
    So, Conductance (G) in a Parallel Circuit will increase when resistance is added and Conductance (G) in a Series Circuit will also increase when resistance is added? I know that Resistance (R) increases in a Series Circuit when additional resistors are added and Resistance (R) decreases in a Parallel Circuit as you add resistors...Because the Series Circuit uses reciprocals for Conductance, does the Conductance decrease as you add resistace?
  4. Adjuster

    Late Member

    Dec 26, 2010
    Words like "added" are likely to be confusing unless you make reference to a circuit configuration, preferably by means of a schematic drawing.

    If you add resistances in series, conductance falls (and resistance rises).

    If you add resistances in parallel, conductance rises (and resistance falls).

    Perhaps you find my reference to conductances in series confusing, as it is not a usual way to deal with these things, but it does complete the picture.

    Note that physically the same device may be described in terms of resistance or conductance, it just depends on how you choose to measure it.
    paul_alan likes this.
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    This is how I teach my students to remember this. As you add conductors in parallel, you have more paths for current to flow. So, since conductance is measured in MHOS, when you have mo' mho, you have mo' current flow. Mo' is mo' better. :)

  6. samin


    Oct 14, 2011
    Conductance resulting from the combination of several resistors connected in parallel is obtained by summing the conductance of each resistor.

    Gt = G1 + G2 + ... + Gn (Gt : Total Conductance , Gn : conductance of the last resistance)

    The values ​​of conductances must all be expressed in the same unit of measure (S or mS or µS)
  7. Wendy


    Mar 24, 2008
    I prefer mhos over the Siemens units myself. S is too close to seconds.