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Author Topic: Magnet Myths and Misconceptions  (Read 547118 times)

Magluvin

• Hero Member
• Posts: 5886
Re: Magnet Myths and Misconceptions
« Reply #135 on: October 10, 2014, 02:56:22 AM »
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

• Hero Member
• Posts: 13958
Re: Magnet Myths and Misconceptions
« Reply #136 on: October 10, 2014, 03:01:31 AM »
MH said,
Quote
"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

• Hero Member
• Posts: 5886
Re: Magnet Myths and Misconceptions
« Reply #137 on: October 10, 2014, 03:13:35 AM »
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

• Hero Member
• Posts: 13958
Re: Magnet Myths and Misconceptions
« Reply #138 on: October 10, 2014, 03:18:55 AM »
MH said,
Quote
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

• Hero Member
• Posts: 5886
Re: Magnet Myths and Misconceptions
« Reply #139 on: October 10, 2014, 03:25:08 AM »
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

Qwert

• Hero Member
• Posts: 924
Re: Magnet Myths and Misconceptions
« Reply #140 on: October 10, 2014, 03:37:35 AM »
MileHigh, I believe, your implication(s) on electrons behavior in DC (Direct Current) in solid conductor are scientifically supported. Can you show us a link or any reference on that matter?

Edit:

Oops! MH, you are supported: http://en.wikipedia.org/wiki/Charge_carrier

Then we have a dilemma.

MileHigh

• Hero Member
• Posts: 7600
Re: Magnet Myths and Misconceptions
« Reply #141 on: October 10, 2014, 04:27:51 AM »
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

TK:

A CRT is a regular circuit with a current loop.  The electrons leave the hot cathode (using FET lingo we can all that the source), and then are accelerated by the anode plates and then strike the phosphor.  Then there is a wire on the side of the CRT that acts as the drain for the electrons to complete the circuit.  I am assuming that there may be a voltage jump when the electrons flow from the drain wire back to the hot cathode to sustain the current loop also.  Sorry, I haven't looked at a CRT schematic in many years.

I don't see where you imply there is an issue.  There is an electric field making the electrons move through the current loop just like there is in a wire in a conventional circuit.  Note also that the beam of electrons can be induced to change direction by either an external electric field or by an external magnetic field.  Isn't it the yoke that produces the raster scan?  (i.e. "deflecting coils.) So the yoke is bending the electron beam because it's generating an external magnetic field where there are two "ramp" stimuli, one for the horizontal and one for the vertical.  I am assuming that there are CRTs that use horizontal and vertical ramp-function voltage potentials to do the same thing.  So instead of a yoke you have two sets of what look like big parallel plate capacitors, one for the horizontal and one for the vertical.

MileHigh

Liberty

• Hero Member
• Posts: 524
Re: Magnet Myths and Misconceptions
« Reply #142 on: October 10, 2014, 04:44:03 AM »
TK:

A CRT is a regular circuit with a current loop.  The electrons leave the hot cathode (using FET lingo we can all that the source), and then are accelerated by the anode plates and then strike the phosphor.  Then there is a wire on the side of the CRT that acts as the drain for the electrons to complete the circuit.  I am assuming that there may be a voltage jump when the electrons flow from the drain wire back to the hot cathode to sustain the current loop also.  Sorry, I haven't looked at a CRT schematic in many years.

I don't see where you imply there is an issue.  There is an electric field making the electrons move through the current loop just like there is in a wire in a conventional circuit.  Note also that the beam of electrons can be induced to change direction by either an external electric field or by an external magnetic field.  Isn't it the yoke that produces the raster scan?  (i.e. "deflecting coils.) So the yoke is bending the electron beam because it's generating an external magnetic field where there are two "ramp" stimuli, one for the horizontal and one for the vertical.  I am assuming that there are CRTs that use horizontal and vertical ramp-function voltage potentials to do the same thing.  So instead of a yoke you have two sets of what look like big parallel plate capacitors, one for the horizontal and one for the vertical.

MileHigh

"The electrons leave the hot cathode"

Hello Milehigh and TK,

If I recall correctly, I think that the cathode was usually "painted" with a chemical that had a rich supply of electrons available, that when heated with the filament, the electrons would be free to boil on the cathode.  This allowed the tube to have electrons to flow with the high voltage potential of the grid and screens and eventually the plate.

Liberty

MileHigh

• Hero Member
• Posts: 7600
Re: Magnet Myths and Misconceptions
« Reply #143 on: October 10, 2014, 05:15:36 AM »
MH said,
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.

The capacitor will have charge and absence of charge on the two plates.  But the wires that supply the current to the two plates of the capacitor will not have any kind of charge imbalance or charge pressure in them.

"Charge imbalance at opposite ends of the wire to induce current flow" is the wrong way of looking it it.  A better way of looking at it is that electrons at some point in a circuit are at some potential level difference compared to some other point in the circuit.  We typically use "ground" as the reference point.  So some electrons can be at a high potential relative to ground but that does not imply some kind of "imbalance" where there are more bunched up electrons on one side of a wire and less bunched up electrons on the other side of a wire.  Yes that happens in capacitors, but they are a different animal.  Capacitors are energy storage devices.

Here is a simple example:

Circuit A is a 10-volt battery connected to a 1-ohm resistor.   Circuit B is a 1-volt battery connected to a 1-ohm resistor.

Are the electrons more densely bunched or imbalanced in Circuit A as compared to Circuit B?

The answer is no, the electrons are evenly distributed in both cases.  However, there are real differences in the relative potential of the electrons in the two circuits.

Let me just switch to conventional current for the rest of this discussion so I don't have to rework everything in my head.

What's the difference between the two circuits?

When the current enters the negative terminal of the battery in Circuit A, it's "takes an elevator ride up by 10 volts in potential" by the time it exits the battery at the positive terminal.  Then when the current hits the resistor it takes a "steep drop" and convert the potential energy into heat.

For Circuit B, the "elevator ride up" from the battery is only one volt, and the drop is a "not so steep drop" with less heat conversion.

Besides that, the current flow and the electron charge density is all the same in both circuits.

All the battery is doing is giving the current a voltage boost from the chemical reactions taking place.

.... see part two... ->

MileHigh

• Hero Member
• Posts: 7600
Re: Magnet Myths and Misconceptions
« Reply #144 on: October 10, 2014, 05:15:59 AM »
Continued...

So here is a thought experiment:   You have two batteries, one is 12 volts, the other one is one million volts.   There is no load on either battery.

When you look at the positive terminals of either battery, does the million-volt battery have more densely packed electrons on it?   (we will ignore the parasitic capacitance between the two terminals that will cause extra charge to appear on the terminals because we are not talking about that aspect.)

So, in my opinion, ignoring the parasitic capacitive effects, you will not observe any difference between the open-circuit positive terminals of each battery.  Both of the positive terminals, being made of metal, will be electrically neutral.   However, the potential of the electrons on the million-volt battery will be much higher that that of the 12-volt battery.

This is pretty "hard core" and I know my limits and all that stuff so I could be wrong in certain aspects.  By in general sense I am pretty confident that I am right.

Almost all circuits are driven by a voltage source.  That means the electric field is king.  The electric field snakes its way through all of the conductors in a circuit.   Some parts of the circuit, and some wires in the circuit may be at very high potential.  In cases like this you have a very very weak electric field inside the high-potential wires.  At the same time, the relative potential of the overall wire itself can be very high.   So you have a very weak electric field at a very high potential.  That may sound contradictory but in fact it's not.

Where you can get a very high electric field is in a resistor.  In wires the electric field strength is very very low, but in resistors the electric field strength can be very high (when you have a large voltage drop).  Sitting on top of all of this is the potential of any point in the circuit with respect to ground.

So you have two concepts of potential going on at the same time.  The first is the concept of relative potential to ground, and the second concept is the local differential potential.  In a wire the local differential potential is almost always very low.

And driving the whole thing is the electric field snaking its way through the wires.   The electrons are just along for the ride as all of this happens.  They don't get more closely bunched up at high voltage potentials.  If all of the electrons in a place in a circuit are at low potential, or if all of the electrons in a place in a circuit are at high potential, there is no difference in local electron density.

MileHigh

MileHigh

• Hero Member
• Posts: 7600
Re: Magnet Myths and Misconceptions
« Reply #145 on: October 10, 2014, 05:34:23 AM »
"The electrons leave the hot cathode"

Hello Milehigh and TK,

If I recall correctly, I think that the cathode was usually "painted" with a chemical that had a rich supply of electrons available, that when heated with the filament, the electrons would be free to boil on the cathode.  This allowed the tube to have electrons to flow with the high voltage potential of the grid and screens and eventually the plate.

Liberty

There is no such thing as a "chemical with a rich supply of electrons available."   The cathode is effectively two things at the sane time.  It is the secondary load of a transformer, that's how it heats up.  This is completely isolated from the main circuit which is the second component.  The main circuit pumps electrons through the cathode such that they end up striking the phosphor screen.  The main circuit is the source of the electrons.  The main circuit is not even "aware" that the cathode is also a load resistor for the secondary of a transformer.

The heat facilitates the liberation of the electrons, somewhat akin to heating water facilitates the more rapid evaporation of the water.

Liberty

• Hero Member
• Posts: 524
Re: Magnet Myths and Misconceptions
« Reply #146 on: October 10, 2014, 05:53:55 AM »
There is no such thing as a "chemical with a rich supply of electrons available."   The cathode is effectively two things at the sane time.  It is the secondary load of a transformer, that's how it heats up.  This is completely isolated from the main circuit which is the second component.  The main circuit pumps electrons through the cathode such that they end up striking the phosphor screen.  The main circuit is the source of the electrons.  The main circuit is not even "aware" that the cathode is also a load resistor for the secondary of a transformer.

The heat facilitates the liberation of the electrons, somewhat akin to heating water facilitates the more rapid evaporation of the water.

Some tubes use an electrically separate cathode that is heated up by the filament.  Some tubes use the filament itself as the cathode.

Liberty

• Hero Member
• Posts: 524
Re: Magnet Myths and Misconceptions
« Reply #147 on: October 10, 2014, 06:12:29 AM »
There is no such thing as a "chemical with a rich supply of electrons available."   The cathode is effectively two things at the sane time.  It is the secondary load of a transformer, that's how it heats up.  This is completely isolated from the main circuit which is the second component.  The main circuit pumps electrons through the cathode such that they end up striking the phosphor screen.  The main circuit is the source of the electrons.  The main circuit is not even "aware" that the cathode is also a load resistor for the secondary of a transformer.

The heat facilitates the liberation of the electrons, somewhat akin to heating water facilitates the more rapid evaporation of the water.

I was taught that the manufactures use a chemical on the cathode.  If they don't, how does a tube wear out or get weak?  Tubes do become weak performers after a time, as there are tube testers to check their operation.  I always thought that it was because the chemical coating on the cathode eventually wore out after a while due to the heat of the filament.  Or not?

MileHigh

• Hero Member
• Posts: 7600
Re: Magnet Myths and Misconceptions
« Reply #148 on: October 10, 2014, 06:27:54 AM »
You may be right that there is a chemical coating on the cathode that facilitates the liberation of the electrons.  I honestly don't know.  When I read what you say I am wondering if a substance can act as a sort of catalyst for the liberation of the electrons.  But to be clear, "facilitating" is definitely not being a source of electrons.

For testing tubes, the filament can simply burn out like a light bulb.  I am guessing that that happens less frequently then the other failure mode.  That mode being when the tube loses its partial vacuum.  If the tube leaks and air enters, that will block the transmission of the electrons because they need a rarefied partial vacuum medium.

There are probably other failure modes.  I am old enough to remember tube testers being at the local pharmacy!  lol

It's scary to think that soon there will be adults that never saw CRT-based TVs for sale at Big Box stores, and adults that never walked into a video club to rent a movie!

MileHigh

CANGAS

• Full Member
• Posts: 235
Re: Magnet Myths and Misconceptions
« Reply #149 on: October 10, 2014, 07:09:16 AM »
Cangas:

I disagree strongly.  Hopefully this new example will swat this nonsensical belief in literal "lines" or "threads" of magnetic field.  There are NO LINES.  The lines are there ONLY to help you visualize the strength and direction of the magnetic field, and that's all.

Look at the attached diagram.  Do you think that there are real "lines" in the air?  What is your common sense telling you?  Now apply that common sense to magnetic fields.

You can't prove that there aren't pink elephants floating over the sky in the center of Greenland either, but you can use your common sense and not let yourself get led down a garden path because you see lines used as a visual aid in diagrams.

MileHigh

u speed reed dont u

It has been proven that speed readers miss over 90% of the content of the stuff they have fleetingly skimmed over. You have ran that up to either 99% or 100%.

My post blatantly stated that FIELD LINES are a useful MODEL.

My post blatantly stated that FIELD LINES may or may not be real, and cannot be proved to either exist or to not exist per se.

Just what is it that you disagree  with me about?

Do you know, or, do you just try to be disagreeable at any opportunity?

CANGAS 87