principe@iccgcc.decnet.ab.com (09/13/90)
A simple question: Does electrical current posess polarity?
Tony P.wayned@wddami.spoami.com (Wayne Diener) (09/13/90)
>In article <882.26ee58ba@iccgcc.decnet.ab.com> principe@iccgcc.decnet.ab.com writes: >A simple question: Does electrical current posess polarity? > > Tony P. A simple answer. No. -- |---------------------------------------------------------------| | // Wayne D. Diener | | // Spokane, WA | | \\ // This space intentionally left blank. | | \X/ |
grege@gold.GVG.TEK.COM (Greg Ebert) (09/13/90)
principe@iccgcc.decnet.ab.com writes: >A simple question: Does electrical current posess polarity? > > Tony P. Almost sounds philosophical. Current is the flow of electrons, which are defined as having negative charge. I plead ignorance in the field of plasma physics, but I would imagine that the flow of a plasma, either positively or negatively charged, would also constitute a current. [Could a sci.physicist please set me straight ?]. Polarity is the increase or decrease in potential energy between 2 points (but not the _amount_; thats voltage). In my humble opinion, I would say that the existence of an electrical current can only be caused by a difference in potential, thus I would say that current DOES possess polarity. - - - - "Current doesn't flow" "You cant buy watts" ------------------------------------------------------------------------- ##### {uunet!tektronix!gold!grege} "Register to vote, then ## | ## grege@gold.gvg.tek.com vote responsibly" # | # # /|\ # "Support the First Amendment, not those who attack it" #/ | \# #######
whit@milton.u.washington.edu (John Whitmore) (09/13/90)
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.