Magnet Myths and Misconceptions

[MarkE]

Lol
see ya saterday night.

Maybe I will take pictures by then with a compass and using:  an isolated conductor (really one half of a loop), compared to a coax.

[MarkE]

Quote PW.
Ions can carry current.  A beam of protons is deflected in a direction opposite to that of a beam of electrons, so I suspect that a flow of positive ions would produce a magnetic field opposite to that of electrons flowing in the same direction.

This is correct.
Although it may be the charge that gives rise to the magnetic field,it is the motion of the charge carriers that determond the orientation of that magnetic field.

Static charge does not give rise to a magnetic field.  Moving charge gives rise to a magnetic field.  The direction that the charge moves determines the direction that the magnetic field circulates.

[MileHigh]

Tinman:

This is totally incorrect,and i know this for fact. This is the difference between those that read books,and those that actually test this very situation with actual devices. Here is a result of this very situation between iron wire and copper wire. Two identical air core coils wound,one with soft iron tie wire(plastic coated),and one with copper wire. Both wires have exact same OD,and same number of turns. Now which do you suppose created the strongest magnetic field when supplied with the same amount of power?-and im talking180%+ stronger.

One more time, it's not as simple as you think.

For starters, using power as the metric here is absolutely wrong.  And you have done it twice in your recent postings.  The power has no direct affect on this experiment.  The resistive losses in the wire are a secondary effect and are meaningless.  The only metric that is relevant to this experiment and the intention behind it it the amount of current flow.

So, this is arguably a mistake on your part because "you do not read books."  Anybody that has learnt about magnetism would pick up on this issue right away.  Chances are you have been "wrong thinking" about examples like this for years.  In fact a month or two ago Luc did solenoid tests where he was comparing his home made solenoid with a commercial solenoid to measure the pulling force.  I tried dropping hints to him and all the participants in the tread many times about this issue.  This issue is that he was chasing after the wrong variable the whole time, assuming that he was supposed to be doing "pure research" - but nobody got it.  For a couple of weeks he was looking at the wrong data.

Now we are going to move onto the issue at hand - my failure to recognize that there would be a difference in the strength of magnetic field generated by the two different types of wire.

As Mark explained to me, I forgot to account for the increased permeability of the iron wire.  So the iron wire would store some of the magnetic energy inside the wire itself.  With more magnetic energy stored in the wire, there is less magnetic energy stored outside of the wire and hence a weaker magnetic field generated by the iron coil.  This difference in wire types would mean that the iron coil should also have a slightly higher inductance.

Okay, so now that I see where my mistake was, I get it.

Now, let's look at your statement in more detail.

You did the experiment on the bench.  The conclusion was "a copper-wire coil produces a stronger magnetic field than an iron-wire coil."  I am going to assume that other experimenters have observed this also, I have read it before.

Here is the problem:  You could only report your observation, but you didn't know why.  That's a total fail.  Without knowing why you are just flying blind.  In some ways it's even a worse mistake than mine.   And here is the reason why:  Putting the differences in the permeability of the two different types of wire aside for a moment, you should be thinking that the strength of the magnetic field produced by the coil is proportional to the ampere-turns of the coil.   So you have the same ampere turns between the two coils, and yet you observe different magnetic field strengths between the two coils.  There is something ostensibly WRONG there, it "doesn't make sense."  If you are working on the bench, you should recognize that there is a "problem."  A problem is no good, and it must be investigated.  But there is no investigation by the typical forum experimenter about this unexplained discrepancy between theory and observation - and that is a TOTAL FAIL.  The only thing they can do is say the two wires are different but they can't explain it but much worse is they don't even try to explain it.  I doubt that you ever tried to explain it.

I have never done these types of experiments because I had no reason to do them.  However, if I did do the experiment and observed a difference in the magnetic field strengths when they were "supposed" to be the same - that would have stopped me cold in my tracks.   It might have taken me five minutes to figure it out.  It might have taken me twenty minutes, it might have even taken me a whole day - but I would have figured it out one way or the other.

There is an important lesson in this and I hope that you and others take it very seriously.  There is no "my experiment trumps what you read in your egghead books."  That is total bullshit.  The reality is the experiment is in 100% agreement with what is in the books.

MileHigh

[MileHigh]

Quote PW.
Ions can carry current.  A beam of protons is deflected in a direction opposite to that of a beam of electrons, so I suspect that a flow of positive ions would produce a magnetic field opposite to that of electrons flowing in the same direction.

This is correct.
Although it may be the charge that gives rise to the magnetic field,it is the motion of the charge carriers that determond the orientation of that magnetic field.

Books.  And from your quote above you are agreeing with what I said and contradicting yourself with respect to your own previous statement.  So can I assume that your second statement holds and you agree with me?

Beyond that, if you actually have to go to the bench to figure this very basic stuff out, then you have a problem.

MileHigh

[TinselKoala]

Iron wire not only has higher permeability than copper wire, but also it has greater _resistance_. So if you have the same diameter wire, and you make two coils of the same dimensions and turn count, the iron one will have greater total DC resistance. So if you apply the same _voltage_ to the coils, say from your voltage-regulated bench supply, you will have less _current_ flowing in the iron coil. This means less power, of course, and also less magnetic field, because the field depends on ampere-turns, everything else being equal.
So since the turns are equal, one needs to supply more DC voltage to the iron core coil so that the _current_ matches the current at which the copper core coil was tested. Same amp-turns needs _more_ power in the iron coil. Ergo, same power means _fewer_ amp-turns in the iron coil, meaning less total magnetic field. This, on top of the permeability effect.



(What is the permeability of _magnetized_ iron carrying current?      )