Re: Bruce's TPU Theory and Experiments - understanding field lines

[allcanadian]

@Milehigh

Well the iron filings don't lie.

I used to think exactly the same thing and then I understood that the iron filings are effected by both the source magnetic field and each other through magnetic induction. Each individual iron filing is induced with it's own magnetic field then each iron filing parallel to one another repels and each above or below each other attracts each other. Thus it is easy to understand that the magnetized iron filings form lines not because there are lines of force but because each has become a magnet in itself. We can replace the iron filings with long slender cylinder magnets and no large external field and they form lines as well.


Think of it this way, would it be wise to measure the voltage on a conductor if all the voltmeters were not only effected by the voltage but also every other voltmeter. Well no, because all the readings would change every time we added or subtracted a voltmeter.


We cannot measure something accurately when the measuring tool (iron filing) is effected by both the external field and every other measuring tool. A hall effect probe does not have this defect and accurately measures the field at any given position.


I think it is very easy to understand and found it very surprising that so many people could be misled by by such simple effects.


AC

[tinman]

@Milehigh

I used to think exactly the same thing and then I understood that the iron filings are effected by both the source magnetic field and each other through magnetic induction. Each individual iron filing is induced with it's own magnetic field then each iron filing parallel to one another repels and each above or below each other attracts each other. Thus it is easy to understand that the magnetized iron filings form lines not because there are lines of force but because each has become a magnet in itself. We can replace the iron filings with long slender cylinder magnets and no large external field and they form lines as well.


Think of it this way, would it be wise to measure the voltage on a conductor if all the voltmeters were not only effected by the voltage but also every other voltmeter. Well no, because all the readings would change every time we added or subtracted a voltmeter.


We cannot measure something accurately when the measuring tool (iron filing) is effected by both the external field and every other measuring tool. A hall effect probe does not have this defect and accurately measures the field at any given position.


I think it is very easy to understand and found it very surprising that so many people could be misled by by such simple effects.


AC

Well a steel ball between two like field's will be repelled,not attracted to the magnets,so it makes sence that the iron fileings would do the same.
But im with MH on this one-what pole's? or what do you refer to as the pole's?.
The term north pole and south pole were chosen because of the orientation of the magnetic field on earth,and ofcourse we have the north pole and the south pole.
So dose the north pole of the earth have a north magnetic field(as we are calling it)or is it a north attracting field(south field)?.Dose our compusses north needle point to a north field,or a south field?.
Well what we know as the north pole,is actualy magneticly south,and the south pole is magneticly north.

[allcanadian]

@All
Here is a picture to explain what is happening with our iron filings. In frame 1 we can see the basic forces at work, magnets on a vertical axis attract and magnets on a horizontal axis repel. Like poles repel and unlike poles attract, I say poles so everyone knows what I am talking about.

In frame 2 we see a permanent magnet which has induced a magnetic field in our gray iron filings or iron cores which is called "Magnetic Induction". Notice all the iron filings have been induced with a polarity opposite to the permanent magnet, this is because the permanent magnet is the predominant field which has induced each of the individual iron filings.

In frame 3 we see the forces pushing the filings apart on the horizontal axis which is also aligning them on the vertical axis. They are not aligning with some imaginary lines of force they are simply attracting and repelling from the other iron filings with their own induced magnetic fields. Here is an experiment, take two iron rods or bolts and align them parallel to one another on a table. Next move a permanent magnet near the rods from the top, What happens?, they move away from one another because the induced like poles at each end repel one another.

In frame 4 we see the iron filings have repelled from one another on any horizontal axis and attracted to one another on the vertical axis. On the vertical axis the like poles have moved towards one another -- Attraction. Each line of filings attracted to one another vertically also repels every other line of filings because we have like poles opposite one another like this.

Repulsion

N   N
S   S


Attraction

N
S

N
S

Again I must say that it is amazing that a process so fundamentally simple and taught in every high school textbook could lead to so much confusion. It is also important to understand that the fields and forces we know exist in 1" pieces of iron wire in a magnetic field do not magically cease to exist or contradict the laws of physics just because the wires get smaller such as iron filings. The laws of physics still apply it is just that they apply in a way we did not expect.

AC

[Dave45]

The coil was froze powered up with 12v ac

[John.K1]

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