Re: Inductance

[Leigh Palmer <palmer@SFU.CA>]

> By habit, I define the inductance of a circuit element as the ratio of  "V
> sub L"  across that element to the rate of change of current in it,  where
> "V sub L"  is the potential difference that appears only when the current is
> changing.  But lately I've noticed that currently popular textbooks tend to
> define inductance as number of turns times flux divided by current.  Is
> there some reason to prefer this "flux-based" definition?

In my opinion there is every reason to resist the flux-based definition.
As it turns out the flux-based formula is the result of applying the
real definition to a linear inductor with geometry and electrical
characteristics which do not vary in time. While that is an important
subset of all practical inductors, the concept of inductance surely is
applicable to many physical systems which are not simple linear circuit
elements. The "swinging choke" comes to mind immediately, of course,
but astrophysical examples abound as well. Is the correct definition
really too difficult for the bright young mind of a university student?
I think it is not.

While I'm railing against these neosacred cows, let me also deplore the
use of the word "potential (meaning electrical potential) in this or
any other time dependent application. I like to firmly associate the
terms "potential" and "time invariant" with one another. Perhaps "emf"
would be a better choice?

Leigh