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# Question about magnetic flux lines and direction of magnetic field. watch

1. Hi!

I'm studying physics and about that right-hand rule I would like to know why the magnetic field(magnetic flux lines) "spins" around an axis that is the wire. I understand the direction of the current(thumb), is intuitive, but the direction of the magnetic field(represented by the fingers indicating counterclockwise) i don't understand it "spins".
2. (Original post by amanda.castro)
Hi!

I'm studying physics and about that right-hand rule I would like to know why the magnetic field(magnetic flux lines) spins around an axis that is the wire. I understand the direction of the current(thumb), is intuitive, but the direction of the magnetic field(represented by the fingers indicating counterclockwise) i don't understand it spins.
Maxwell's RH rule tells us which direction the magnetic field is directed round a wire carrying current.

The definition of the direction of a magnetic field is the direction that a North monopole (if one existed) would travel.

All that the fingers of your right hand are telling you is that should a north pole venture near a wire carrying a current it would experience a force in the direction indicated by your fingers.
3. (Original post by nerak99)
Maxwell's RH rule tells us which direction the magnetic field is directed round a wire carrying current.

The definition of the direction of a magnetic field is the direction that a North monopole (if one existed) would travel.

All that the fingers of your right hand are telling you is that should a north pole venture near a wire carrying a current it would experience a force in the direction indicated by your fingers.
I'm sorry but I don't understand the last part. Maybe is my english.
All that the fingers of your right hand are telling you is that should a north pole venture near a wire carrying a current it would experience a force in the direction indicated by your fingers.
Could you explain that in another words?
4. It's because of centripetal force
5. (Original post by GUMI)
It's because of centripetal force
Are you serious?
6. Nothing to do with centripetal force. If a north monopole goes near a current carrying wire it will experience a force. If you were inside the wire following the conventional current the force would cause the north monopole to move around you in an anti clockwise direction.
7. This is what maxwell right hand rule is describing.
8. (Original post by amanda.castro)
Hi!

I'm studying physics and about that right-hand rule I would like to know why the magnetic field(magnetic flux lines) "spins" around an axis that is the wire. I understand the direction of the current(thumb), is intuitive, but the direction of the magnetic field(represented by the fingers indicating counterclockwise) i don't understand it "spins".
I know there should be a good explanation for this that doesn't just rely on equations (should probably involve a relativistic argument and/or conservation of energy) but I can't think of it right now.

That said, there is a straightforward reason if you know Gauss' law - this says that the total flux going out of a surface is proportional to the net charge inside the surface. For electric charges, this means that if you have a positive charge, then field lines will be going outwards through a surface drawn around the charge, and inwards for a negative charge.

For a current carrying wire, there are no magnetic monopoles (they don't exist) so there should be NO NET FLUX through a surface drawn around it (a cylinder will do). But we know the the field needs the same shape all around the wire due to the symmetry of the situation, so it must be circling.

But yes, if someone could construct an explicit example of why radial field lines would let you violate conservation of energy that would be a better explanation.

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