AndrewS

I would like to ask a seemingly daft question. What is the experimental evidence for the traditional magnetic flux, as described by people such as Faraday, Maxwell and Fleming?

We need to bear in mind that this magnetic flux was based on an ignorance of magnetism - orbiting and spinning electrons were unknown 150 years ago. I have asked in vain for evidence of this flux. It seems to be just a guess which turned into a belief.

Suppose magnets had been unknown at the time. Experiments with electricity would then have led to a simple law: like currents attract and opposite currents repel. This basic law then explains magnetism, such as the alignment of iron filings around a magnet. Imagine for example that two bar magnets have stuck themselves together side by side, i.e. with north poles touching south poles. The circulating charges in the two magnets are, at their closest, moving in the same direction - a bit like cog wheels meshing together. Hence there is a net force of attraction.

Using Ockham’s principle, the complication of a circular perpendicular field is then unjustified. (Instead of Biot and Savart’s law to predict flux density, the attraction between elements of two current vectors is dF = k I1.I2 ds1 ds2 /r^2 where k depends on the permeability.) So magnetic forces just act along the straight lines between moving charges. This is the same simple principle that works for electrostatic forces between stationary charges. We need not assume the universe uses two completely different force mechanisms. Motion just modifies the electric field.

Traditional magnetic fields are defined as continuous. So the field emanating from the north end of a bar magnet loops round the outside of the magnet to the south pole and returns through the magnet’s body back to the north pole. Now imagine a magnet made of a very viscous material that allows a free-moving north pole to drift within it. This internal north pole would be repelled by the magnet’s south pole (?) and leave again through its north pole. We are all taught this stuff, but it doesn’t make sense to me. We should not view magnets as perpetual motion machines. Forces begin and end at points: they do not keep going round in circles. There is a measurable energy gradient along a real force field, but there can be no such gradient around a continuous loop.

Magnetic flux represents the total "lines of force" through a surface, but no force can be detected along these lines. The notion of circular fields perhaps arose when rings of iron filings were seen around a conducting wire, but it was a very odd idea. The circular magnetic field at any point is defined as a vector that is perpendicular to the force it produces. However, if a vector represents something that measurably exists, e.g. a physical force, a wind velocity, a flow of energy or a stampede of hamsters, its perpendicular components are zero. So we can say that a magnetic field having its greatest effect in a perpendicular direction does not exist.

oz93666

Good to question everything ....Physics as we know it has many errors....

I think it's just the word 'flux' which is leading to confusion ...it can imply a flow .... no one would suggest anything is flowing anywhere.

When people map out the 'flux' of a magnet it's just a picture of magnetic pull or push on another magnet at that particular point, and the direction of that force ... twice the flux , twice the pull/push ...

So don't blame Maxwell and others , they are just drawing out what the compass shows .

AndrewS

Thanks for your reply.

Compass needles behave in accordance with the law that like currents attract and opposite currents repel. They provide no evidence of a field acting in the wrong direction. The measurable forces, i.e. not Maxwell's "lines of force", act in the same direction as the electric force. Motion just modifies the electric field. What is the evidence that a magnetic field exists perpendicular to the force it is meant to create? Is there any experimentally verifiable field that produces a force in a perpendicular direction?

If it helps, ignore my use of the word flux and substitute field.

oz93666

I'm not sure I follow you .... currents don't attract or repel ...magnetism (which currents create) does ......

A coil of wire with a current is indistinguishable from a permanent magnet ...

Spell out more clearly your issue with established methodology ...

AndrewS

Thanks again, but I'm not sure I can spell it out more clearly. You have already seen the point I am making, i.e. currents do attract and repel and the force can be calculated without reference to a perpendicular field.

Let's imagine that magnetite and magnets hadn't been discovered and that people in the 19th century were experimenting with your coil of wire. With two coils they would soon arrive at the conclusion that like currents attract. When atoms etc. were later discovered this simple law would then explain your permanent magnet. In this scenario we would not now be encumbered by the rigmarole of Fleming's rules etc. School kids need not be deterred from studying physics and engineering by having to remember which fingers of which hand to poke in which direction. The basic law of magnetism is quite simple.

The problem arose not just because people didn't understand what lay behind magnetism, i.e. like currents attracting, but they thought magnetism was a different force to electrostatics. Hence they were looking for two different fields. My point is there is one field. Motion just modifies the electric field.

If you want a further criticism of traditional methodology I would say it involves a contradictory assumption about a major and arbitrary asymmetry in the behaviour of electrons. Any experiment that seems to support Maxwell's corkscrew can equally be said to prove its exact opposite, i.e. the corkscrew is left handed and Fleming should have used his other hand. This assumed asymmetry seems to be unverifiable. I'm not sure it should even be classed as a scientific hypothesis.

oz93666

I sort of get what you are saying ... but I can't envisage a world without the left hand rule engineers would still need it to know which direction a conductor will move in a magnetic field

AndrewS

Engineers would be delighted to avoid the mumbo-jumbo of Fleming's rule.

It is best to forget about magnetic fields. Motion just modifies the electric field. I know it's very difficult to ditch long held beliefs, especially when we are quite pleased we managed to get our heads round them in the first place.

A further problem with this unfortunate historical misunderstanding was the emphasis on magnetic poles. People understood the properties of these poles but not much else. People naturally assumed a pole was a thing, many people still do, but a pole is no more a thing than is a clockwise. A pole is merely a convenient label for a circulating charge.

Treating poles as things results in the nonsensical picture of a bar magnetic with a free internal pole being repelled by a south pole. Firstly there are no free poles - poles are not things - and secondly a pole is both north and south. When you look at the other side of a south pole it is a north pole. This is obviously because from one side of a circulating current the charges move clockwise and from the other they are anticlockwise. In a rational world the poles of magnets could be labelled C and A.

To return to your example of an engineer contemplating the forces on conductors, imagine a square circuit. The current on opposite sides of the square is moving in different directions so these sides repel each other. What could be simpler?

It did briefly occur to me that that Faraday et al may just have been having a laugh. If they believed in an afterlife they could look forward to giggling at countless generations of puzzled students poking their fingers needlessly in the air. If no one can provide evidence to support the traditional magnetic field it seems far more likely that this is just an irrational belief passed down the generations from a time of understandable ignorance.

By the way, when calculating forces there is no need to perform a double integral of the current vectors in one go, as the above equation may suggest. The traditional calculations can still be done in stages. One just needs to accept that a current does not produce a separate magnetic field. Instead of calculating a non-existent magnetic field one is calculating a modification of an electric field. Motion just modifies the electric field. The assumption of two separate fields to explain a single force appears to be groundless.

AndrewS

As no one has provided any evidence that traditional magnetic fields exist, nor even that they qualify as a scientific hypothesis, it looks like we can agree they do not exist.

studiot

Here is a simple (in engineering terms) question

In a scrapyard a crane with a large electromagnet lifts cars to the crusher.

How much current is required to lift a car of mass m?


I would be interested to see your improved solution over applying the theorem of virtual work to the magnetic field.

AndrewS

I'm pleased to see you are not saying that a separate magnetic field exists.

The answer to your question depends on the design of the electromagnet, but the maths would give the same answer. The difference being that any reference to magnetic fields is replaced by changes to the electric field.