# Does a single electron have poles?

1. Oct 26, 2009

### kashiark

If so, why? Shouldn't it attract positive charges equally from all sides?

2. Oct 27, 2009

### lstellyl

The electron is taken to be a point particle. As a point charge, it has a coulomb potential that emanates radially from it's position.... so yes, it will attract any positively charged particle equally from all sides (so long as we are considering positive charges of equal charge)

you may have been thinking of electron spin? if not, ignore that comment...

3. Oct 27, 2009

### Bob_for_short

An electron is an electric monopole and a magnetic dipole. Three poles in total.

Last edited: Oct 27, 2009
4. Oct 27, 2009

### kashiark

What are the properties of these poles, and from where do they originate?

5. Oct 27, 2009

### Bob S

Measurements of the electron electric dipole moment show that if there is one, it is less than 7 x 10-28 e-cm, meaning that it is equivalent to less than two opposite electron charges separated by 10-28 cm. i.e., zero to the best measurements made. See electrons in
http://pdg.lbl.gov/2009/tables/rpp2009-sum-leptons.pdf
Bob S

6. Oct 27, 2009

### Bob_for_short

The electric monopole is a source of electric (Coulomb) field and the magnetic dipole is a source of the magnetic dipole field of electron. They are features of nature, experimental facts.

7. Oct 27, 2009

### kashiark

What exactly is an electric field? Does the electron unevenly attract positive charges and/or unevenly repel negative charges?

8. Oct 27, 2009

### Bob_for_short

I will tell you exactly what an electric field is. It is a force divided by charge. In other words the product of electric field and charge is the force standing in the right-hand side of the Newton equation: ma = qE. There is no other way of understanding an electric filed - it is what appears in the charge equation of motion as an external force.

For two charges you have to write two equations of motion. Each equation contains an external force created with an external source. For particle 1 it is the electric force of the second particle. For particle 2 it is the electric force of the first particle. Depending on charge signs, the forces can be attractive or repulsive.

9. Oct 27, 2009

### kashiark

That makes sense, but this is what I'm confused about:
"Magnetic dipole
A model of an object that generates a magnetic field in which the field is considered to emanate from two opposite poles, as in the north and south poles of a magnet, much as an electric field emanates from a positive and a negative charge (each of which is a monopole) in an electric dipole."
How can a single electron have a magnetic dipole? I don't understand.

10. Oct 27, 2009

### Bob_for_short

It's easy. You can consider it as a spinning ball of a small but a finite size, so the charge motion creates an electric current and a dipole magnetic field. Like a current loop. (Any spinning planet has one).

Last edited: Oct 27, 2009
11. Oct 27, 2009

### kashiark

Ah, ok that makes sense. Thanks!