Polarity of Wire: North/South Poles?

[ritwik06]

Homework Statement

There is a straight current carrying wire. A magnetic field is produced round the wire. Will north pole and south pole be developed?

 

[Dick]

Where would they be? All magnetic flux lines are closed. What do N and S poles really mean? Questions to ponder.

 

[ritwik06]

Where would they be? All magnetic flux lines are closed. What do N and S poles really mean? Questions to ponder.

I think they would be on the opposite sides of the wire. I mean if we cut the cylindrical wire(small diameter) along its diameter, we would get two separate parts of equal length which were north pole and south pole previously. Am I right?

I don't know what north poles and south poles exactly mean.

 

[Dick]

You talk about poles where the magnetic field has the form of a dipole, like a solenoid or a bar magnet (like the Earth's magnetic field). If you put a compass on the Earth it points towards one pole and away from the other. I get your point about cutting along diameters, but if you follow a compass located near the wire, it will just lead you in circles around the wire, not to any definite region. That's my interpretation anyway.

 

[ritwik06]

You talk about poles where the magnetic field has the form of a dipole, like a solenoid or a bar magnet (like the Earth's magnetic field). If you put a compass on the Earth it points towards one pole and away from the other. I get your point about cutting along diameters, but if you follow a compass located near the wire, it will just lead you in circles around the wire, not to any definite region. That's my interpretation anyway.

Well, I seem to understand your point. You might mean to say that in this case magnetic field exists without any poles at all. But really are you sure that what I said is wrong?? Think of a bar magnet and solenoid. Magnetic field lines are continuos inside the solenoid and I think I am not wrong if I say that it is true for a bar magnt too. What do you think?

 

[Dick]

All magnetic field lines are continuous. There is really no exact definition of a 'magnetic pole' that I know of. And I think you can only even vaguely define them if the field has a dipole configuration. A dipole is generated by a circulating current. A current flowing a straight wire doesn't circulate. Hence no dipole. That's what I would say. How does your book or instructor define 'magnetic pole'? If you don't have a definition of the word it's hard to decide. But as for the diameter, you can cut along ANY diameter and get the same field picture, right? So where were the poles before you cut?

 

[ritwik06]

Well, i really have no idea. it seems complicated...