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Author Topic: Magnet Myths and Misconceptions  (Read 605741 times)

synchro1

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Re: Magnet Myths and Misconceptions
« Reply #1410 on: January 20, 2015, 08:01:42 PM »
It isn't.

Strength of a magnetic field is measured in Tesla units or Gauss.

verpies

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Re: Magnet Myths and Misconceptions
« Reply #1411 on: January 20, 2015, 08:08:36 PM »
"Pull-force on a test piece of iron is not the same thing as the strength of the magnetic field".
It is true. A linear "pull force" on a piece of iron depends on the gradient of magnetic flux density, and a torque acting on a magnetic dipole (e.g. a bar magnet)  depends on magnetic flux density and the sine of the angle that the dipole forms with the B field's direction.

This is nothing but complete bullshit. All magnetometers work on the principle of attraction to magnetic objects
No, for example the Hall sensor works on the principle of Lorentz deflection of electric charges.  The Hall sensor is sensitive to the magnetic flux density and the angle to the B field, unlike iron which is linearly sensitive only to the flux density gradient. 
Because of this difference it is possible for a Hall sensor to give a very high reading while a piece of iron placed in the same location will not experience any linear attraction force.

verpies

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Re: Magnet Myths and Misconceptions
« Reply #1412 on: January 20, 2015, 08:14:15 PM »
Strength of a magnetic field is measured in Tesla units or Gauss.
Actually those are units of magnetic flux density. (a.k.a. "B field")
It is possible for a piece of iron to experience zero linear force in a high magnetic flux density, because the iron reacts linearly only to its gradient.

synchro1

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Re: Magnet Myths and Misconceptions
« Reply #1413 on: January 20, 2015, 08:27:57 PM »
It is true. A linear "pull force" on a piece of iron depends on the gradient of magnetic flux density, and a torque acting on a magnetic dipole (e.g. a bar magnet)  depends on magnetic flux density and the sine of the angle that the dipole forms with the B field's direction.
No, for example the Hall sensor works on the principle of Lorentz deflection of electric charges.  The Hall sensor is sensitive to the magnetic flux density and the angle to the B field, unlike iron which is linearly sensitive only to the flux density gradient. 
Because of this difference it is possible for a Hall sensor to give a very high reading while a piece of iron placed in the same location will not experience any linear attraction force.

@Verpies,

The Hall effect sensor simply produces a voltage proportional to the applied magnetic field. The strength of the magnetc field is measured in gauss: "The gauss, abbreviated as G or Gs, is the cgs unit of measurement of a magnetic field B, which is also known as the "magnetic flux density" or the "magnetic induction".

"The most common magnetic sensing devices are solid-state Hall effect sensors. These sensors produce a voltage proportional to the applied magnetic field and also sense polarity".

One gauss is also equal to 10−4 kg C−1 s−1. Notice the Kg value in the gauss equation. This represents "Kilograms of pull force".
This value alone is the sole value of magnetic field strength.

Hall effect sensor voltage is directly proportional to the "pull force" of the applied magnetic field.

MileHigh

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Re: Magnet Myths and Misconceptions
« Reply #1414 on: January 20, 2015, 08:55:52 PM »
Synchro1:

MarkE, Verpies, and myself are correct and you are wrong.  I am sure that Picowatt would join our club also.  What I suggest you do is look over what has been stated and do some searching on those terms and find the information and learn it.  If there are people that are interested in magnetism and the terms "magnetic flux," "magnetic flux density," and especially the term "magnetic field gradient" make you just "zone out" and just skip it, you can't.  Just do the work and hopefully come back better informed.

MileHigh

picowatt

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Re: Magnet Myths and Misconceptions
« Reply #1415 on: January 20, 2015, 09:08:38 PM »
Synchro1:

MarkE, Verpies, and myself are correct and you are wrong.  I am sure that Picowatt would join our club also.  What I suggest you do is look over what has been stated and do some searching on those terms and find the information and learn it.  If there are people that are interested in magnetism and the terms "magnetic flux," "magnetic flux density," and especially the term "magnetic field gradient" make you just "zone out" and just skip it, you can't.  Just do the work and hopefully come back better informed.

MileHigh

Agreed,

I particularly liked Verpies' recent posts.  Accurate, succinct, and to the point.

PW



verpies

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Re: Magnet Myths and Misconceptions
« Reply #1416 on: January 20, 2015, 09:15:59 PM »
One gauss is also equal to 10−4 kg C−1 s−1. Notice the Kg value in the gauss equation. This represents "Kilograms of pull force".
This value alone is the sole value of magnetic field strength.
No, kilogram is not a unit of force.  Anyway in that formula you have kilograms per second, which is mass change.  :o
Xavier Borg has even different units for flux density if that amuses you.

Hall effect sensor voltage is directly proportional to the "pull force" of the applied magnetic field.
No, Hall effect sensors can give a high indication even when a piece of iron placed in the same location experiences no linear force.
Ergo, they don't measure the same thing.

picowatt

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Re: Magnet Myths and Misconceptions
« Reply #1417 on: January 20, 2015, 09:22:28 PM »

One gauss is also equal to 10−4 kg C−1 s−1. Notice the Kg value in the gauss equation. This represents "Kilograms of pull force".
This value alone is the sole value of magnetic field strength.


Synchro1,

Consider why there is a capital "C" in the cited formula...

PW

MileHigh

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Re: Magnet Myths and Misconceptions
« Reply #1418 on: January 20, 2015, 09:54:18 PM »
Damn I just lost a posting.  I don't know why but it's agony to recompose a posting that you just lost.  In a nutshell I was apologizing because I know that sometimes I flub my units, like "magnetic flux gradient" vs. "magnetic field gradient."  I may sometimes say "magnetic flux" when I really should be saying "magnetic flux density," etc.  I only did this stuff in school, including the bench work.  It was a long time ago.  I don't think and breathe this stuff at all.  As a result my technical vocabulary and the use of the proper technical terms and concepts can be less than stellar at times.  I know the terms and pretty much understand them, but the proper technical prose to describe something does not flow like it does from some of you guys.  Sometimes I will go back to the Hyperphysics web site to brush up but I don't really go that deep.  So I have my own "zone out" threshold.  So I apologize again and please feel free to correct me if I make a mistake.  When in doubt, defer to the really big guns around here.

picowatt

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Re: Magnet Myths and Misconceptions
« Reply #1419 on: January 20, 2015, 10:59:02 PM »
Damn I just lost a posting.  I don't know why but it's agony to recompose a posting that you just lost.  In a nutshell I was apologizing because I know that sometimes I flub my units, like "magnetic flux gradient" vs. "magnetic field gradient."  I may sometimes say "magnetic flux" when I really should be saying "magnetic flux density," etc.  I only did this stuff in school, including the bench work.  It was a long time ago.  I don't think and breathe this stuff at all.  As a result my technical vocabulary and the use of the proper technical terms and concepts can be less than stellar at times.  I know the terms and pretty much understand them, but the proper technical prose to describe something does not flow like it does from some of you guys.  Sometimes I will go back to the Hyperphysics web site to brush up but I don't really go that deep.  So I have my own "zone out" threshold.  So I apologize again and please feel free to correct me if I make a mistake.  When in doubt, defer to the really big guns around here.

MH,

Yes, the connection error thing is quite annoying.  Seems to be getting worse.

As for the rest of your post, none of us are infallible.  It is often easy to "misspeak" and worse yet, at my age, I am a bit of a rusty nail when it comes to topics I have not dealt with to any great degree for many years. 

However, the formula Synchro1 posted "One gauss is also equal to 10−4 kg C−1 s−1" to me reads as "One gauss equals 10-4kg per Coulomb per second".  Hopefully someone will correct me if I am wrong, but I believe that is the acceleration a conductor will experience while passing 1 Coulomb at a right angle to a flux of 1 gauss. 

As I said, I could be wrong, so hopefully someone will comment a bit further and better than I...

MarkE?  Verpies?

PW




tinman

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Re: Magnet Myths and Misconceptions
« Reply #1420 on: January 20, 2015, 11:33:52 PM »
Tinman:




MileHigh
Quote
Okay, for starters, one thing that you have to realize is that experimentally you have an "advantage."  You do the experiment, you see it in front of your own eyes, you try different things, and it all seems pretty clear to you.  Then you give us a few sentences that are typically just results and the barest of any description at all.  Realistically, there are going to be limitations in what you get in terms of feedback and in my head I have to "invent" the setup and the details of what I _think_ might be going on and you can see all the pitfalls that happen on both sides because of that.
It wasnt my intention to give a full description of my test,i was simply stateing that i had done this very test,and i wanted to know if you knew what the outcome would be.

Quote
If in the future you want to discuss another experiment and explore the theme of "books vs. bench" then the much better way to do that would be to make a good video clip of it.  And I have to fire a warning shot across the bow here.  No verbal description of your circuit.  If you are not willing to make a schematic for tests that involve some kind of circuit then forget it.  You probably have some old clips on your channel where you do a verbal run-down describing 10 to 15 connections and it just doesn't fly.
Are you saying that you need a full schematic of a DC power supply,AMP meter and a coil?-you wouldnt be able to follow that in a video description?.

Quote
I read Mark's comments about the pull force and the possible increased curl giving you a higher gradient close to the poles.  That might mean that there is a stronger pulling force only in close proximity to the poles.  It might mean that the attraction force dies off very quickly with distance for the "stronger" coil and for the "weaker" coil the attraction force extends out much further.  We have zero data so it's all an unknown.
Quote post 1416:  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.

Quote
If the difference was very minimal, then I could ignore your incorrect reference to power dissipation,
Once again,as to where did i give any power disipation meassurements for the circuit setup?. I used only P/in.

 
Quote
It's like you are saying this to us:  I have two identical copper coils driven from the same voltage source.  The first coil is in series with a 10-ohm resistor and the second coil is in series with a 20-ohm resistor.  Which coil produces the stronger magnetic field?   Can you see what I am saying how that's a bullshit experiment?
No,it's not like im saying that at all. We are useing two different materials in the same configuration to see which gives rise to better results for the same P/in. The resistance is a value associated with the different materials used-nothing we can do about that if we wish to use these two different materials.

Quote
If the currents in the two coils are significantly different, then the whole test is in a sense BS.  Yes, I am using strong terms.  It's because if you are comparing how two coils of the same geometry will produce a magnetic field, then you want to have the two coils have the same current going through them.  This is something you should know and you should have set up your experiment like this.

No No No.
When we want to know what coil will give the best results for a machine that requires a certain field strength  from our coil to opperate at close proximity to that coil for the least P/in,then the test was done correctly.
Once again-the P/in was the same.

Quote
After factoring everything in, the real experiment here is to test your two coils with the same current going through each coll.  Then, if you are going to measure the attraction force for each coil, you need to measure what it looks like along the axis of the coil at perhaps five or more distances from a pole.  That puts the two coils on a level playing field.
No,the real test was to supply the two coils with the same P/in,and test the pull/attraction force of each coil at close prximity.

 
Quote
I have to assume that when you are at a "far distance" from the the poles of the respective coils, that you will measure a stronger magnetic field from the copper coil.

As i mentioned in reply to TK's post.

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

With 20/20 hindsight,it is clear that you decided to make assumptions about my test without knowing anything about it. For what i wanted to know,the test was carried out correctly,and gave me the exact results i needed to know. And to say i cant do a test correctly,and base that assumption on incorrect assumptions, is the BS you are after.

Quote
My final thought which I think you avoided is to go back to the permeability issue.  That is sound and makes sense and I thank Mark for mentioning it.  If you did a proper test setup like I mention above, I am not talking pull force, I am talking doing a compass test or something like that to see which field is stronger.  Will you feel a stronger attraction force up close for the iron coil?  What Mark said about the curl sounds plausible.  I would measure the forces and also do an iron filings test to look at the curl and gradient of the magnetic fields from the two coil.

The test setup was correct for the information i required. I have already agreed that the magnetic field from the copper coil was probably much larger,and the iron wire would have concentrated the field around the coil.

tinman

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Re: Magnet Myths and Misconceptions
« Reply #1421 on: January 20, 2015, 11:55:29 PM »
 
Quote
No, kilogram is not a unit of force.
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.

verpies

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Re: Magnet Myths and Misconceptions
« Reply #1422 on: January 21, 2015, 12:04:29 AM »
As I said, I could be wrong, so hopefully someone will comment a bit further and better than I...
MarkE?  Verpies?

You can interpret the Tesla in so many ways, it's not funny.
...and don't forget the Xavier Borg's blog while you're at it  ;)

verpies

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Re: Magnet Myths and Misconceptions
« Reply #1423 on: January 21, 2015, 12:06:56 AM »
Where:

m = meter
s = second
kg = kilogram
A = Ampere
V = Volt
C = Coulomb
J = Joule
N = Newton
H = Henry
Wb = Weber

tinman

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Re: Magnet Myths and Misconceptions
« Reply #1424 on: January 21, 2015, 12:08:52 AM »
TinMan
Some light reading directly related to misconceptions  . And perhaps a method to harvest energy
From some heretofore difficult venues....?

http://bovan.net/gmweb2/The%20FS%20Loop.htm.  (From a friend of Yours )


Enjoy


Chet
Just started reading this Chet,and im hooked already.
How true is this book.
1 verse-quote:
Also, most folk seem to forget that when they are but one in a crowd of like minded and consensus deriving thinkers, everyone still has individual and personal responsibility for what they themselves believe, and thus for all of their actions which result from their beliefs, whether these appear to be majority determinations or not.  Yet whilst some individuals do not know what questions to ask in order to develop a fundamentally correct comprehension, or are maybe unwilling to be recognised for being seen to ask an important question which might upset many egotists or activists within their group (yes, even in science), with the result that many follow blindly without asking or thinking, or accept that they ought not ask when told to not do so, no one can achieve a usefully realistic understanding without provision being made for the answering of each and every question posed.  So in relation to formative learning, we ought not rely solely upon explanations provided exclusively by the hierarchical and subjectively imagined hypotheses which led to the development of qualified "expert" opinion, but instead strengthen foundations by building upon irrefutable findings via the objectively established and openly truthful reporting of observation and occurrences, also repeat testing, demonstration and experimentation, such that we might beware a collection of isolated facts becoming joined together in a manner which misrepresents fundamental truth, due to our minds having been conditioned in a manner which makes it difficult to see beyond any 'power presentation' of anything we are told;  as especially with relation to the fundamental nature of electromagnetic-radiation itself.

Lets await the onslaught.