# Is a proton a magnet?

1. Nov 11, 2006

### davidong3000

i know electrons have spin and charge which makes them the smallest magnet. protons also have spin and charge. does this mean they are magnets too with a north and south pole?

Precisely where are these poles in relation to the spin axis of the proton and electron?

Last edited: Nov 11, 2006
2. Nov 11, 2006

Staff Emeritus

Yes, protons are magnets, and they precess. So do neutrons oddly enough. In spite of having no charge, they have a magnetic moment, due to the charged and spinning quarks inside them (the quarks' charges cancel out in the neutron, but add in the proton). These facts are behind the chemistry analytical tool NMR, for nuclear magnetic resonance, and that in turn is behind the medical device MRI, magnetic resonance imaging.

3. Nov 12, 2006

### davidong3000

so if i was looking down on the axis of an electron/proton in such a way so that it appears to be spinning anti clockwise, would i be looking at the north or south pole?

4. Nov 13, 2006

### Meir Achuz

The magnetic moment of the proton is in the same direction as its spin, so its N pole would be on top. The electron magnetic moment is oppositeto its spin direction because the electron is negatively charged.
Its top pole is a S pole.
Note, even though these particles have "spin", they are not rotating.
They are said to have spin because they have angular momentum.
This follows from relativistic QM (the Dirac equation) without their actually rotating.

5. Nov 13, 2006

### davidong3000

Can u define "top"?

Last edited: Nov 14, 2006
6. Nov 15, 2006

### Meir Achuz

The north pole would be at the "top" of the earth.
By "top" I meant where the head of the arrow woud be in the right hand rule for rotation. (If fingers curl in direction of rotation, the vector omega is in the direction of the thumb.)

7. Nov 15, 2006

### vanesch

Staff Emeritus
And actually the magnetic "pole" of the earth on the north pole is ...
a magnetic south pole !

8. Nov 15, 2006

### davidong3000

so earth is like a giant electron then . xcept earth is not - charged. both earth and electrons have their s pole on top according to rh rule.

so exactly how many teslas are single electrons and protons spitting out? and do the magnetic fields of these charged particles loop back on themselves from top to bottom like on ordinary magnets?

Last edited: Nov 15, 2006
9. Nov 19, 2006

### Meir Achuz

The second answer is yes.
The first answer is a bit messy to calculate, but I get that the B field at the proton in hydrogen due to the electron's magnetic moment is about
one million tesla.

10. Nov 22, 2006

### davidong3000

what if it didn't have an electron? say a lone proton or lone electron, what would the tesla reading be?

11. Nov 25, 2006

### Meir Achuz

I used the H atom just as an example for the B field a distance of 1/2 angstrom away from a lone electron. The B field would fall of like 1/r^3, so an electron's B field would be about 100,000 T 1 angstrom away.
The B field of a proton would be about 600 times smaller than that of an electron at the same disstance.