# What is magnetic pole? What is sink/source?

1. Dec 10, 2009

### marion.s

What is the definition of 'magnetic pole' and 'sink/source'? Same thing?

Are there any experiments and equations that can locate magnetic poles?

How far away are magnetic north and south poles of single spinning electron?

2. Dec 10, 2009

### darthoctopus

There are monopoles and there are dipoles. Monopoles are sinks/sources (e.g. point masses, charges) which give a nonzero divergence. Magnetic dipoles (the type you find in solenoids, say) give zero divergence because on the whole they are neither sources nor sinks. So no, they are not the same thing.

Um, I suppose you could wave a Hall probe around in space. I don't think it's very meaningful to point to something and call it a magnetic pole in the same sense as you could with one half of an electric dipole, precisely because there are no sources/sinks. I guess this probably renders the electron thing moot too.

3. Dec 10, 2009

### Bob S

Some people have built particle detectors to search for magnetic monopole "rays", pull monopoles out of meteor dust (and moon dust?), and even built the magnetic equivalent of a toroidal electric circulating current, using ground-up meteor dust in balls of epoxy. No monopoles found.
Bob S

Last edited: Dec 10, 2009
4. Dec 10, 2009

### marion.s

F= k* q1*q1/r^2

F= k* m1*m2/r^2

These equations describe both poles and sources/sinks of electric and gravity fields to be in the same location, so why is that not the definition of what poles and source/sinks are - the points of attraction/repulsion?

How do you define "field pole"? How do you define "sink/souce?

How do you call the place in a magnetic field towards which opposite magnetic field gets attracted to? Why is that not a sink?

5. Dec 10, 2009

### marion.s

How do you define "pole"? How do you define "sink/source"?

How far away are magnetic north and south of a single electron?

Do magnetic field lines actually go through poles or circle around them?

6. Dec 10, 2009

### marion.s

Superposition of magnetic fields

Looking at a single electron as a source of magnetic dipole moment we may notice that even though these two magnetic poles have to be extremely close to each other the magnetic fields do not cancel out as electric fields would. What are the principles, definitions and equations describing superposition of magnetic fields?

7. Dec 11, 2009

### kcdodd

without magnetic charges, magnetic field lines form closed loops. The term "pole" is just a convenience of orientation of the magnetic field with respect to a coordinate system. It doesn't mean there are actually poles, as in charges. "dipole moment" contains the same type of information: orientation of magnetic field in coordinate system.