# Understanding Conductance in Circuits

#### paul_alan

Joined Nov 5, 2011
43
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.

Joined Dec 26, 2010
2,148
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...)

#### paul_alan

Joined Nov 5, 2011
43
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?

Joined Dec 26, 2010
2,148
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

#### KL7AJ

Joined Nov 4, 2008
2,229
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. Eric

#### samin

Joined Oct 14, 2011
32
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)

#### Wendy

Joined Mar 24, 2008
22,544
I prefer mhos over the Siemens units myself. S is too close to seconds.