Magnet Myths and Misconceptions

[Magluvin]

  I first figured out how current through a static magnetic field forced the current carrying metal to move by reading a very old book published around 1901 dealing with electromagnetism.  It was a practical guide for electric motor technicians and engineers.  Below is a picture I drew up fast to duplicate the much better diagram from the book.  The magnetic field is like water blowing across the ocean surface.  In the diagram this is from left to right.   The conductor current is flowing into the page.   (could be out long time since I did any right-hand left hand stuff)   A circular flow of magnetic current is created as indicated by the arrow around the conductor surface.   The rotating current increases the total magnetic pressure on top of the conductor whereas it decreases the magnetic pressure below the conductor.  Therefore the conductor moves from the top of the page to the bottom.  Something like an airplane wing or a sail.  The wind because of it's viscosity has to travel faster around the bulge in the wing or sail.  This decreases the pressure.   The lower side of the wing or the more or less flat side of the sail allows the wind to flow unimpeded and at a velocity less than the air traveling the bulge.  The split stream converges at the trailing edge of the wing or sail at the same velocity as the bulk flow of air relavent to the craft.  Anyway the pressure is greater under the wing than it is on top and this lifts the craft up as the ambient pressure continually tries to fill the partial vacuum created by the fast moving air. 

Hey Sparks

I have not played with iron wire coils yet, but supposedly they do produce a field with current. Its interesting what you are saying.

Say we run dc through a straight iron wire and we build a field around the wire, just like copper wire(I think), and if when we remove that current, is it possible that the iron wire could maintain at least some of the field in the orientation it was when current was flowing. Sort of like how a soft iron nail can retain a magnetized state N and S from end to end, is it possible for the iron wire to maintain a circular field around the wire after the current is removed.  Say we hit the wire with a momentary high discharge that creates an initially large field around the wire, would there possibly be any remanence of that field after the discharge ceases? A circular field with no true N or S ends to it. Dunno. But interesting thought.

Mags

Mags

[TinselKoala]

MH said,

"When you pass DC current through a conductor there is no "Newton balls" phenomenon taking place.  To me "Newton balls" implies electrons enter one end of a conductor and "push" on adjacent electrons to form a chain reaction where electrons at the opposite end of the conductor get "pushed out."  That is not happening."

Oh? What if the end of that wire is connected to the cathode of an electron gun in a CRT? Where do the electrons in the beam come from, if not from out of the wire supplying the cathode?  Or have you gone over to the TA side, where you don't believe that there is a beam of electrons, focussed and directed by changing magnetic fields, in a CRT?

http://en.wikipedia.org/wiki/Cathode_ray

[Magluvin]

Hey Sparks

I have not played with iron wire coils yet, but supposedly they do produce a field with current. Its interesting what you are saying.

Say we run dc through a straight iron wire and we build a field around the wire, just like copper wire(I think), and if when we remove that current, is it possible that the iron wire could maintain at least some of the field in the orientation it was when current was flowing. Sort of like how a soft iron nail can retain a magnetized state N and S from end to end, is it possible for the iron wire to maintain a circular field around the wire after the current is removed.  Say we hit the wire with a momentary high discharge that creates an initially large field around the wire, would there possibly be any remanence of that field after the discharge ceases? A circular field with no true N or S ends to it. Dunno. But interesting thought.

Mags

Mags

A possible secondary experiment would be to apply enough current to heat the iron wire pretty good, then freeze the wire with freeze spray while removing the current. 

off that topic, I had an idea to wind a copper wire around a plastic toroid, 4in dia, 1/2in thick, 1/2in deep.  1 layer. Then make a rotor with all magnets N pointing out. just used 2 mags in the test.  It was a slap together thing, a bit off balance in every way, but just tried.  When I applied current to the coil, sometimes the rotor turned CW, sometimes CCW.  The idea was to have the mags close to the inside part of the coil and have the N poles of the mags ride the field spin around those inner windings.  As in a DC motor without pole switching. I chose to use a non magnetic core so as not to have it absorb the field away from the mags.  But a core may help, havnt gotten there yet. Busy with life. Try to get to some experiments here n there. Just throwing it out there.


Mags

[TinselKoala]

MH said,

NO because you can't "charge" the conductor because you are implying this conductor forms part of a circuit.  There is no net charge on a conductor that forms part of an electrical circuit.

Charge up a capacitor with DC. The plates of the capacitor and the conductors connected to them have a net charge, equal and opposite since charge is a conserved quantity. Install the capacitor in an AC oscillating circuit and the plates and conductors attached to them will have net charges, alternating polarity as the capacitor charges and discharges and recharges in the opposite polarity. Right?

Current flow in a conductor is basically a process of equalizing charge pressure between more positive and more negative unbalanced regions. Only when current stops flowing is charge equalized; conversely, no current flows unless there is a charge imbalance between the ends of the wire. So if you look at a wire carrying current with a very sensitive instrument you will see a voltage drop along the wire, because the wire has a finite resistance. This means that there is a charge imbalance between the ends of the wire, that exists and that can be measured as long as current is flowing in the wire.

[Magluvin]

MH said,
Oh? What if the end of that wire is connected to the cathode of an electron gun in a CRT? Where do the electrons in the beam come from, if not from out of the wire supplying the cathode?  Or have you gone over to the TA side, where you don't believe that there is a beam of electrons, focussed and directed by changing magnetic fields, in a CRT?

http://en.wikipedia.org/wiki/Cathode_ray

Also if we look at a wire run  from one place to another over a great distance, when we apply a current to one end of the wire, there is a latency as to when the other end of that wire produces output vs 'when' the input was introduced.  Say ground for return.  So it can be just like Newtons cradle and not all electrons moving in the wire at the same time, but a crowding at the input of electrons that eventually expands reaches the other end over time, depending on polarity. the input could be depleting electrons from the input end of the wire creating a lack of electrons at the input and yada yada yada.

Mags