Magnet Myths and Misconceptions

[MarkE]

1kg is equal to 9.81N,and newtons are a messure of force. Is this splitting hairs? or are we to stick to the !1kg is an amount of mass that exerts a force of 9.81N on the earths surface?!.
Seems to me that saying 1kg of force is exactly the same as saying 9.81 newtons of force when used here on earth. This would however change in space where there is no gravity,as you can have mass but no weight.

You;ve got the idea.  To be a bit more pedantic:  A kg is a unit of mass that is the same anywhere in the universe.  On average, at sea-level on earth a kg is subject to 9.81N force towards the earths CoG due to gravitational acceleration.

[MileHigh]

Tinman:

Sure I made some assumptions about your test.  We can't survive if we don't make assumptions.  Look, there is a commonality of thinking in a given discipline.  It promotes communication and allows for discussing things with commonly accepted terms and understood frames of reference.

You said that you were a trucker?  When you are driving at night and one truck wants to pass another truck, the truck in behind will flip off his headlights for a 1/4 second when he is ready to make his move.  Then the truck up ahead will flip off his running lights for 1/4 second to acknowledge the passing request so everybody is cool and both drivers know what is going on.  Is that right?  I think it works like that.  Well, what if you wanted to pass and instead and you flashed your high beams three times?  That would mess things up, no?  If I recall correctly flashing your high beams three times means "a big thank you."  I don't remember the exact code but it's something like that.  Now, the average driver in a car is not even aware of the code.  But if you are a long-haul trucker or an inter-city bus driver you sure as hell better know the code.  It's for safety and your life could depend on it.

Now you said that you wanted to compare the magnetic fields from two different coils that were the same physical dimensions and wire gage but one was iron and the other one was copper.  I know that you said for the same power but we are going to put that aside for a second.  When you say that, what is a person that is experienced in electronics going to say to themselves?  Well, they hear "compare coils for magnetic field" and "same dimensions" then the fist thing that they are going to think is that you must have the same current flowing through each coil so that you have the same number of ampere-turns for each coil.  It's another variation on the trucker code.  This is what makes sense, this is what would be expected.  You said that you wanted to compare the magnetic fields after all.

When you do have the same current flowing through each coil, then you have the proverbial level playing field.  The experiment then becomes a question of checking how the wire itself affects the generation of the external magnetic field around the two coils.  You have one wire with a relative permeability of one and the other wire with a relative permeability of about 1000.  Now you have a controlled experiment for looking at and comparing the magnetic fields around the two coils based on the wire itself.

You can state that for the above type of test you want to ignore the resistance of the wire itself because the resistance of the wire is an easily to eliminate variable.  The resistance of the wire does not directly affect the generation of the magnetic field of the coil so you eliminate that as a variable.  The resistance of the wire only indirectly affects the generation of the magnetic field.

The simple fact is that you did not propose the test with the proper terminology.  We are back to "the code" again.  The real intention of your test was to see how the wire gage would affect the power dissipation in two different types of coils for certain magnetic field strength.  That's really what you are talking about, and it's not the test that I stated above.

Something like this:

For the same magnetic field generation for a copper coil of the same number of turns and dimensions:

Gauge      Watts
36           8
24           6
16           4

For the same magnetic field generation for an iron coil of the same number of turns and dimensions:

Gauge      Watts
36           22
24           18
16           13

In other words, you can take a copper coil, and for the identical magnetic field generation, choose almost any power dissipation you want (within limits) by adjusting the diameter of the wire itself.

For an iron wire, it's similar but a bit more complicated because as the diameter of the wire increases, you will be able to store progressively more magnetic energy in the wire itself.  So you don't necessarily have the the identical external magnetic field generation as you increase the diameter of the wire.  It's a second variable that complicates things.

But do you see my point?   It was the same thing with Luc's test.  He was testing "watts required for a given pulling force."  One more time you can dial up any wattage you want just by changing the diameter of the wire.  In the context of what he was trying to research, he should have been testing ampere-turns vs. pulling force.

You want to push back the deeper you get into electronics and go your own way.  The better way of going about it would be to at least try to understand what is going on first before you reject it.  I am talking in general terms here.  Mark said you have your "own ideas" about magnetics and coils and stuff like that.  Everybody is speaking the same language in the world of electronics, why do you want to speak your own language, especially if you are wrong about something?  The real solution is to give it a shot and push yourself and see if it starts to become clearer for you.  Eventually you start speaking the same language and using the same "code."

Again, you simply did not express yourself properly with respect to what you really wanted to do.  Yes, copper and iron have different resistances.  So it's self evident that you will have to put more voltage across the iron coil to get a similar (but not identical) magnetic field generation.  In the truest sense that has nothing to do with "comparing different wire materials for magnetic field generation."

Like many things in life Tinman, you have to get with the program.  It doesn't mean that you are "locked in" and can't do certain experiments.  It just means that you have to use the same communication tools and concepts that everybody else uses in order to be effective.

MileHigh

[MarkE]

To be fair:  Tinman did say that he used the same number of turns.  He did say that he used iron wire.  And he did say that he operated at constant power.

[MileHigh]

To be fair:  Tinman did say that he used the same number of turns.  He did say that he used iron wire.  And he did say that he operated at constant power.

But then he should have stated the fact that the coil resistances were significantly different.  I had no clue.  The last time I might have even looked at that would have been in the back of a textbook in 1980.

[MileHigh]

Tinman:

You chopped my sentence up half-way.

"But with 20-20 hindsight it's now apparent to me that you can't do a test yourself"

vs.

"But with 20-20 hindsight it's now apparent to me that you can't do a test yourself and see it and play with it, and give us pop quiz questions without us seeing the same tests ourselves."

Do you get the meaning in what I said?  It probably could have been worded better bit it is what it is.

MileHigh