Magnet Myths and Misconceptions

[TinselKoala]

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

[tinman]

Tinman:



MileHigh

You did the experiment on the bench.  The conclusion was "a copper-wire coil produces a stronger magnetic field than an iron-wire coil

."

How ever did you come up with that MH?.Where in my post did i say that the copper wire coil produced a stronger magnetic field?.
Quote: Now which do you suppose created the strongest magnetic field when supplied with the same amount of power?-
How on earth did you come up with a conclusion(which is incorrect by the way)from my statement>?

Here is the problem:  You could only report your observation, but you didn't know why.  That's a total fail.

A total fail MH is saying that there was a conclusion to my test,when it was insted a question directed at you

Without knowing why you are just flying blind.  In some ways it's even a worse mistake than mine.

I made no mistake MH,you did in some how deciding that i gave a conclusion to my test.

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

There is nothing wrong there. Do you think that the soft iron wire has the same resistive value as the copper wire for the same gauge of wire?. And do you think then that the ampere turns value remains the same? Did you miss the part where i said-Quote: when supplied with the same amount of power.

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.

Have you gone completely nut's MH>? To check the difference in magnetic field strength of two coils useing two different types of wire to obtain data that shows the best performer for the same P/in. As we are useing DC,then power is an accurate description.

So, this is arguably a mistake on your part because "you do not read books

Nope,it was your mistake because you didnt read the post correctly.

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.

No again.
It about creating a stronger magnetic field for the same P/in

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

And no
My test are correct-your asumptions are wrong.

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.

Nothing to do with me.

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.

There you go,the difference between the bench and book's. The soft iron wire had more pull force on my piece of key steel than the copper wire coil did. It was the soft iron wire coil that had near 180% more pull force than the copper wire coil for the same P/in.

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.

The problem MH here is that some how you came to a conclusion in my test,that was made from a question-and was also incorrect.

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.

I am trying to work out how you think my experiment was wrong before i gave the results-which i have now posted above in the comments.
This is becoming a habbit here on this thread-guys replacing my statements with things i never said-just like you have done here MH.

I will stick to my bench MH,and see the true results right there in front of me-->you keep to your books.
My respect remains for you MH,but you have to stop turning things i say!like this! quote: -Now which do you suppose created the strongest magnetic field when supplied with the same amount of power?-, into this-Quote: The conclusion was "a copper-wire coil produces a stronger magnetic field than an iron-wire coil.

[tinman]

   



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

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.

Exactly TK.

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

.
The very reason i used the term power  in-the same amount of power  was supplied to the two coils during my test.

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.

Indeed.

Ergo, same power means _fewer_ amp-turns in the iron coil, meaning less total magnetic field. This, on top of the permeability effect.

I went higher in voltage until the P/in was the same as that of the copper coil.
But my test showed a much stronger magnetic pull force for the same P/in from the soft iron wire coil.-This is opposite to what your saying TK?. I believe the reason for this is because the field is much more concentrated around the iron coil. The field around the copper coil may well have been much larger in size-this i didnt check.

[MarkE]

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?      )

But the gradient at the end of the magnet should be much higher on an air core because even with fewer A*T, the flux curls much more severely to the iron wire with its high permeability.  So lifting strength of the magnet picking up a piece of soft iron should be much higher than copper wire on an air core.  But test it for strength using a soft iron solenoid plunger in the middle and the results will be very much as you describe.

[MarkE]

Exactly TK.
.
The very reason i used the term power  in-the same amount of power  was supplied to the two coils during my test.

Indeed.
I went higher in voltage until the P/in was the same as that of the copper coil.
But my test showed a much stronger magnetic pull force for the same P/in from the soft iron wire coil.-This is opposite to what your saying TK?. I believe the reason for this is because the field is much more concentrated around the iron coil. The field around the copper coil may well have been much larger in size-this i didnt check.

It's the curl in the field at the end of your coil that is sharper and that is giving the greater lifting force on soft iron near the pole.  Now, think about what you are observing in your test:

You have lower current, but higher permeability.  So the magnet as a whole has less field at TK says, but it folds over more tightly at the end.  Do these observations support your idea of magnetic charges, the conventional view, both, or neither?