Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Current as Vector



Brian wrote:

I certainly can find counter examples to the assertion that resistance
is a scalar. Plastic films show notable non isotropism.

You don't need exotic materials to make resistance "dependent" (in some sense) on "direction." For instance, what is "the resistance" of a 1 cm x 2 cm x 3 cm block of graphite?

Nevertheless, in my book, resistance is a SCALAR property of a) a given object and b) a well-specified electrical connection scheme*. If the object is anisotropic, the anisotropy is expressed through a conductivity TENSOR relating the local current density (a VECTOR) to the local electric field (another VECTOR). That anisotropy is taken into account along with the connection details when determining the SCALAR resistance.

* I recognize that resistance may also be a function of applied voltage, temperature, and perhaps other things, but that doesn't detract in any meaningful way from the point I am trying to make.

--
John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>