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Re: [Phys-l] Current as Vector




On Mar 22, 2006, at 12:49 PM, John Denker wrote:

Herbert Schulz wrote:

Vectors behave in certain ways under addition, etc.

That is an important consideration, and a good way to frame
the discussion.

I recognize the existence of both:
-- A vector current J, and
-- A scalar current I.

Arguing about which of these should be called "the" current reminds
me of the holy war between the big-endians and the little-endians.

I don't see how
current can be a vector since it doesn't add like vectors; e.g., two
currents do NOT add like vectors at branch points in circuits.

Really? I would say that they DO behave like vectors; in particular
the physical significance of "I" cannot be established except by reference
to a chosen basis vector.

For details, see
http://www.av8n.com/physics/resistance.htm#sec-diag

As it says there:

]] Let’s be clear:
]]
]] * The vector current J has direct physical significance.
]] * The scalar current I is convenient for calculations.
]] * The physical significance of I cannot be established except by reference
]] to some chosen basis vector.
]] * You are free to choose your own basis vector, but you should be prepared
]] for the possibility that other people will choose differently. This is
]] harmless, so long as everyone clearly communicates what choice they have made.

Howdy,

I guess I've always heard J referred to as the Current Density Vector (it has a magnitude with units of Current/Area; e.g., Amp/m^2) not the Current (I). I thought that I (through a given surface) = Surface Integral of J\cdot dS over that surface.

Good Luck,

Herb Schulz
(herbs@wideopenwest.com)