# Homework Help: Analogy Between Conductance & Capacitance

1. Dec 14, 2007

### Mo7amed

Hi all...
I want more information about the analogy between calculating the capacitance C and the conductance G ?

2. Dec 14, 2007

### TVP45

I don't think that's an analogy. The formulas may appear somewhat similar simply because of how things are added in parallel or series, but that's just an algebraic thing.

3. Dec 14, 2007

### mda

There's a physical reason underlying the similarity of the equations, which is that they are related to transport properties. Whilst this similarity exists for all such properties, these two are particularly similar in that they both relate to the electric field via the constituent equations

$$D = \epsilon E$$
$$J = \sigma E$$

Following through to C & G, we get

$$C = \epsilon A / d$$
$$G = \sigma A / d$$

Using basic geometric arguments you can then derive series & parallel relationships.

If one assumes time-harmonic fields these become very closely related through the concept of complex permittivity.

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