🚀 go-pugleaf

In article <882.26ee58ba@iccgcc.decnet.ab.com> principe@iccgcc.decnet.ab.com writes:
>A simple question: Does electrical current posess polarity?
>
        In the sense that it has a direction?  Yes, the magnetic
field around a wire obeys the 'right-hand rule', so a compass
will deflect in a way that identifies the current direction of a
nearby wire.

	In the sense that the charge carriers can be identified as (+)
or as (-), yes; two techniques exist for doing this.  The most common
is the Hall effect; some odd effects in the presence of a magnetic field
result in a conductor getting a transverse electric polarization when
it conducts electricity, and this effect depends (in polarity) on the
identity of the charge carriers' sign.  More exotic, a relativistic
synchrotron generates synchrotron radiation; there is a strong
beam of radiation in the direction of travel of the electrons (or
positrons- the synchrotron I use has both).  A simple measurement of
the beam current shows the sum of electrons-going-clockwise with
positrons-going-counterclockwise, but the synchrotron radiation 
coming out of the beam at a tangent is mainly 'forward' with
respect to the velocity of the charges generating it.  A beam
of positrons sheds most of its radiation in the opposite
direction to a beam (carrying the same measured current) of
electrons.  This only happens for relativistic currents, though,
and the symmetry is not broken until the kinetic energy of the
charges approaches their rest mass ( 500,000 eV for an electron
or a positron; more for protons and the like).
	It may seem that only electrons carry current in a
wire, however; this is not entirely true, as the Hall effect
shows; some of those electrons have such heavy constraints on
their motion that a simple theory of their movement requires either
that we ascribe negative mass, or positive charge, to them.
These, then, are the infamous 'holes' that show up in semiconductor
electronics.

	In the sense that power carried by an electric current
can be given an unambiguous direction?  Yes; the so-called
Poynting vector, generated by the cross product of the magnetic
and electric fields always points in the energy-movement
direction.  Remember, ANY current generates a magnetic
field, and by Ohm's law, any current in a conductor implies a
nonzero electric field as well.

	Current is measured in units of electric-charge-per-second,
by identifying the total transfer of charge through some area
(like the bore of a synchrotron or the cross section of a wire),
and is definitely a signed quantity; this sign is the orientation
of the surface area under consideration to a directional current.


I am known for my brilliance,             John Whitmore
 by those who do not know me well.