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Effect On Faraday's And Other Laws If You Define B In The Opposite Direction - Does Nature Have Ours Hardwired In It?


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#1 Jonathan212

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Posted 01 July 2019 - 03:26 AM

Suppose there were a people on Australia that had not had any contact with us up until the middle ages, and they had developed their own science where they drew maps upside down and their campuses pointed to their version of north: the Antarctic. Then they would have drawn magnetic lines pointing towards the Antarctic. Whereas ours point towards the Arctic (click on image to see direction in theirs).

 

Image2.jpg

 

But wait, one day the Australians would have discovered the motion of charged particles in a magnetic field and come up with Faraday's law of induction that looked like this:

 

electromotive force (emf) E = dΦ / dt

 

whereas ours is:

 

electromotive force (emf) E = - dΦ / dt

 

where Φ = integral( integral( B . dA ) )

 

The negative sign is explained as the result of Lenz's law: "Nature abhors a change in flux". But it is missing in their version. As if Lenz's law does not apply to those Australians... evidently the two conventions are not as good. Other laws of physics would be messed up too with negative signs popping up all over the place or disappearing.

 

So is the choice of north pole arbitrary, or does nature really have ours hardwired in its laws?


Edited by Jonathan212, 01 July 2019 - 03:32 AM.


#2 VictorMedvil

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Posted 01 July 2019 - 03:36 AM

Suppose there were a people on Australia that had not had any contact with us up until the middle ages, and they had developed their own science where they drew maps upside down and their campuses pointed to their version of north: the Antarctic. Then they would have drawn magnetic lines pointing towards the Antarctic. Whereas ours point towards the Arctic (click on image to see direction in theirs).

 

attachicon.gifImage2.jpg

 

But wait, one day the Australians would have discovered the motion of charged particles in a magnetic field and come up with Faraday's law of induction that looked like this:

 

electromotive force (emf) E = dΦ / dt

 

whereas ours is:

 

electromotive force (emf) E = - dΦ / dt

 

where Φ = integral( integral( B . dA ) )

 

The negative sign is explained as the result of Lenz's law: "Nature abhors a change in flux". But it is missing in their version. As if Lenz's law does not apply to those Australians... evidently the two conventions are not as good. Other laws of physics would be messed up too with negative signs popping up all over the place or disappearing.

 

So is the choice of north pole arbitrary, or does nature really have ours hardwired in its laws?

 

Now this has to do with the movement of electrons, if it was opposite the electrons would move in the opposite direction, but actually electrons move in a certain direction based on that negative sign there in front.

 

bar.gif

 

Do you see the field lines, the field lines would be opposite if the negative was not there.

 

5.png


Edited by VictorMedvil, 01 July 2019 - 03:40 AM.


#3 exchemist

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Posted 01 July 2019 - 03:54 AM

Suppose there were a people on Australia that had not had any contact with us up until the middle ages, and they had developed their own science where they drew maps upside down and their campuses pointed to their version of north: the Antarctic. Then they would have drawn magnetic lines pointing towards the Antarctic. Whereas ours point towards the Arctic (click on image to see direction in theirs).

 

attachicon.gifImage2.jpg

 

But wait, one day the Australians would have discovered the motion of charged particles in a magnetic field and come up with Faraday's law of induction that looked like this:

 

electromotive force (emf) E = dΦ / dt

 

whereas ours is:

 

electromotive force (emf) E = - dΦ / dt

 

where Φ = integral( integral( B . dA ) )

 

The negative sign is explained as the result of Lenz's law: "Nature abhors a change in flux". But it is missing in their version. As if Lenz's law does not apply to those Australians... evidently the two conventions are not as good. Other laws of physics would be messed up too with negative signs popping up all over the place or disappearing.

 

So is the choice of north pole arbitrary, or does nature really have ours hardwired in its laws?

Choice of N and S is arbitrary, as is the direction of electric current (what we call an electric current flows in the opposite direction to the actual charge carriers, as these are electrons, which confusingly we give a -ve charge to.)

 

But whatever sign conventions our notional Australians come up with, it will have to explain the observed effect that, if you have two parallel wires carrying a current in the same direction, the associated magnetic field will cause them to repel one another.  This is the simplest electromagnetic phenomenon, so if their sign convention predicts this result correctly, all the rest will work fine as well.   


Edited by exchemist, 01 July 2019 - 03:56 AM.


#4 Jonathan212

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Posted 01 July 2019 - 04:10 AM

So it is not by chance that we have called proton motion a positive current to go with a positive emf induced by a negative B, but they were all chosen to make equations neat?


Edited by Jonathan212, 01 July 2019 - 04:11 AM.


#5 Jonathan212

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Posted 01 July 2019 - 04:26 AM

Here's another law that would be messed up without our version of north. Lorentz force:

 

F = q E + q v x B

 

It would become

 

F = q E - q v x B

 

to get the same force direction which translate into motion direction and motion direction is not by convention, it is objective.



#6 VictorMedvil

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Posted 01 July 2019 - 04:29 AM

Here's another law that would be messed up without our version of north. Lorentz force:

 

F = q E + q v x B

 

It would become

 

F = q E - q v x B

 

to get the same force direction which translate into motion direction and motion direction is not by convention, it is objective.

 

See it would change the laws of physics that's why it has to be that way.



#7 exchemist

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Posted 01 July 2019 - 05:37 AM

So it is not by chance that we have called proton motion a positive current to go with a positive emf induced by a negative B, but they were all chosen to make equations neat?

No they were chosen to make them work, not to be neat. By "work" I mean able to account for the repulsion between the parallel wires I mentioned.



#8 Jonathan212

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Posted 01 July 2019 - 11:25 AM

You sure about that? I thought the repulsion does not require any one of the conventions mentioned, they all end up with repulsion, it works with all of them: positive electron or negative electron, positive B pointing to the Arctic or the Antarctic.

 

But there is a case where the conventions matter or so it seems, and that is when the magnetic field appears as an electromagnetic wave. Electrons in a receiving antenna follow the Lorenz force and our convention makes neater equations.


Edited by Jonathan212, 01 July 2019 - 02:16 PM.


#9 Jonathan212

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Posted 01 July 2019 - 02:19 PM

Or the Australians could change both B and q and E and get the same F = q E + q v x B we do. So something is hardwired in nature's laws, you must have a certain relation between the directions assigned.

 

The cross product too is a convention, the direction of the result could also be defined to be the opposite. So what seems to be hardwired is a set of combinations of q sign, E direction, B direction and cross product direction.


Edited by Jonathan212, 01 July 2019 - 02:21 PM.


#10 exchemist

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Posted 02 July 2019 - 12:53 AM

You sure about that? I thought the repulsion does not require any one of the conventions mentioned, they all end up with repulsion, it works with all of them: positive electron or negative electron, positive B pointing to the Arctic or the Antarctic.

 

But there is a case where the conventions matter or so it seems, and that is when the magnetic field appears as an electromagnetic wave. Electrons in a receiving antenna follow the Lorenz force and our convention makes neater equations.

Well yes of course, nature is what nature is. All I meant was that so long as the system of sign conventions gives the right answer physically, that is all that matters. We're agreed about that. 

 

And yes I suppose cross product (from which we get the left hand and right hand rules in electromagnetism) is also a matter of convention, just as it is a convention that a screw travels away from you when you turn it clockwise.



#11 Jonathan212

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Posted 02 July 2019 - 06:11 AM

All I'm saying is not all conventions are of equal value when it comes to solving physics problems, therefore we should consider the possibility that some are profoundly wrong, or all are profoundly wrong except the one we've converged to over centuries. One could solve problems robotically like an engineer and get correct answers without pondering at all about whence the equations came.