Electron spin

[Chriss]

I can't really understand electron spin. Is it rottation along it's axis ? Thanks !

[swansont]

It's not physically spinning. Spin is intrinsic angular momentum.

[Chriss]

And what is spin up and spin down.

[swansont]

And what is spin up and spin down.

 

Those are the two possible orientations of the electron spin. You pick an axis for measurement, and the projection along that axis will be either + or - one unit of angular momentum (Planck's constant). We call that up or down.

[Chriss]

What n, l, m and s values refer too ?

[imatfaal]

What n, l, m and s values refer too ?

 

Do you have the context or even better a link from which those letters are taken - there are only so many letters and they get re-used in different topics

[swansont]

n is the principle quantum number, aka the energy level

l is the orbital angular momentum quantum number

m is the magnetic quantum number, which is the projection of the orbital angular momentum on the quantization axis. l ≥ |m|

i.e. a n electron in an l=1 state can have m = -1, 0 or 1

s is the spin quantum number for a system with spin S. Similar to the m and l relation, a spin 1/2 particle can have s = ±1/2

[Chriss]

These image says that electron it's spinning around it's axis.

http://www.google.ro/imgres?imgurl=http://www.magnet.fsu.edu/education/tutorials/magnetminute/images/emr.jpg&imgrefurl=http://www.magnet.fsu.edu/education/tutorials/magnetminute/emr.html&h=307&w=398&sz=9&tbnid=CiTPXXYn8idAeM:&tbnh=90&tbnw=117&zoom=1&usg=__ecmvSdllUzubgBAnYjpVv3yc1BA=&docid=cMVzmWK6FNN0NM&sa=X&ei=ACZyUrvHJInHsgavnoH4Dg&ved=0CGEQ9QEwBg

[swansont]

These image says that electron it's spinning around it's axis.

http://www.google.ro/imgres?imgurl=http://www.magnet.fsu.edu/education/tutorials/magnetminute/images/emr.jpg&imgrefurl=http://www.magnet.fsu.edu/education/tutorials/magnetminute/emr.html&h=307&w=398&sz=9&tbnid=CiTPXXYn8idAeM:&tbnh=90&tbnw=117&zoom=1&usg=__ecmvSdllUzubgBAnYjpVv3yc1BA=&docid=cMVzmWK6FNN0NM&sa=X&ei=ACZyUrvHJInHsgavnoH4Dg&ved=0CGEQ9QEwBg

 

 

It's wrong. A physically spinning electron would require it's rotation to exceed the speed of light.

[Chriss]

What about the magnetic propreties of electron ? Are the electrons of two types: North magnetc pole and South magnetic pole ?

[swansont]

Electrons are dipoles, so they behave like a bar magnet, with both a north and a south pole.

[Chriss]

So how the magnetic filed are created by moving charges ?

[swansont]

So how the magnetic filed are created by moving charges ?

 

That's one way of creating magnetic fields, and a classical notion. Fundamental particles are quantum particles, so they have properties without having the actual classical behavior. Spin is angular momentum, as if it were spinning, but without the classical motion. A spinning charge would give you a magnetic field.

[Chriss]

So electrons already have magnetic moment north and south, and when they are flowing they create a magnetic filed by the right hand rule if i understand well ?

 

What about magnets ?

[swansont]

 

What about magnets ?

 

What about them?

 

Permanent magnets are materials (like iron) where the electrons' magnetic moments line up and also have a macroscopic structure where the atoms can be held in a fixed position, ensuring the fields add.

[Chriss]

So in a magnet all the electrons in an atom ar orbiting clockwise or counter clockwise ? I am a little bit confused. And i don't intend to bother someone.

 

I think i started to get it. In every orbit there are two electrons one spinning clockwise and one counter clockwise. Hmm...

So what happens in a magnet is that on one side of the magnet all electrons that not have a match on the orbit are spinning in one direction and on the other pole of the magnet all electrons that not have a match spin in oposite direction ?

Thanks !

Edited October 31, 2013 by Chriss

[Enthalpy]

All centers in the same direction is impossible, because if one aligns up, its side neighbours will naturally align down.

 

But in ferromagnetic materials like soft iron or hard magnets, the neighbours have different strengths, so that one over two aligned up and the next down results in a net global field. It can also be local electrons up and shared electrons down.

[swansont]

All centers in the same direction is impossible, because if one aligns up, its side neighbours will naturally align down.

 

But in ferromagnetic materials like soft iron or hard magnets, the neighbours have different strengths, so that one over two aligned up and the next down results in a net global field. It can also be local electrons up and shared electrons down.

 

No, in iron there are unpaired electrons in the d shell. Hund's rule says that these will have the same spin. That's the source of the net field for a single atom. The fact that the iron atoms can connect such that neighbor atoms add to the field is what allows it to become a permanent magnet.

[Chriss]

Is it a relation between electron spin and direction in wich is rotating on the orbit clockwise or counter clockwise. My question is in wich direction is spinning electron with spin up (clockwise or counter clockwise) ? Thanks !

[swansont]

A particle that is spin up has angular momentum in the up direction. There is no actual rotation.

 

Classically this would be the result of the right-hand rule, which would be counter-clockwise rotation if you were looking at the vector, i.e. down.

[Chriss]

I wanted to post something which now i don't !

How do i delete this post ?

Edited November 2, 2013 by Chriss

[Chriss]

What i didn't understood well is Stern Gerlach experiment. And my question is that they found out that electrons have a north and south pole magnet, and half of them went up and half down trought the magnets ? I know that they shoot silver atoms, so how they know about the electrons spin ?

Edited November 12, 2013 by Chriss

[swansont]

It's not that half went up and half went down, it's that the deflection was a set amount rather than a continuum. Which means that the magnetic moment (resulting from the intrinsic angular momentum) was quantized in value and in orientation, which is not a classical result.

[Chriss]

How they knew about electrons if they shoot atoms ? and also why they didn't shoot electrons with an electron gun ? (it wasn't knew ?)

[swansont]

How they knew about electrons if they shoot atoms ? and also why they didn't shoot electrons with an electron gun ? (it wasn't knew ?)

 

They knew that electrons are in atoms. You don't want to use electrons because they are charges, and will deflect in a magnetic field as a result of the moving through it. Atoms are neutral, and the only deflection would be from the inherent magnetic moment.