Is SPIN a calculated or physically measureable characteristic?

[Whovian]

It's impossible to visualize spin. Just think of it as a property. Some people think of it as a particle spinning about an axis, and while spin is technically angular momentum, this can be very misleading under some circumstances..

 

[ajayguhan]

then what does "orbital angular momentum " and "orbital dipole momentum" refers to..?.orbit is region of space where there is a probability of finding an electron.does a space aslo have angular momentum and dipole momentum as spin...?

 

[Whovian]

I suspect this may be misleading, but I have a feeling it isn't.

A way to visualize orbital angular momentum would be this. Take an object, put it on the end of a massless rope, swing it around. (A bit unrealistic, but the point still holds.) The orbital angular momentum will refer to the angular momentum from the spinning of the ball. In this case, orbital angular momentum would probably refer to the angular momentum of an electron from orbiting an atom's nucleus. Orbital dipole momentum I'm probably not the one to ask about.

 

[radioactive8]

One more question ...
I know that the magnetic forces come from the electrons spin ... i want to know how can this happen ... Why are magnetic forces cauzed by the electrons spin ... ?

 

[Simon Bridge]

radioactive8: It's more that we deduce the existence of the electron's spin by its reaction to a magnetic field. It is part of the QM properties of the electron - the wavefunction has a magnetic moment component.

Whovian: Electrons do not "orbit" their nuclei and electrons outside an atom still have spin.

ajayguhan: the terms are a historical leftover from the Bohr model of the atom. Quantum Mechanics has to have equivalent terms in order to replace Bohr theory.

We have to be careful making classical analogies of quantum behavior ... QM is a superset of classical mechanics so there will be some quantum phenomena that just cannot be modeled classically. That's why we have it. At some stage you just have to accept that quantum mechanics is weird - but accurate.

 

[kith]

One more question ...
I know that the magnetic forces come from the electrons spin ... i want to know how can this happen ... Why are magnetic forces cauzed by the electrons spin ... ?

Classically, magnetic fields are caused by currents. An electron with orbital angular momentum is moving and thus causes a current and a magnetic field.

In QM, we have a new type of angular momentum, which is a intrinsic property of particles independent of motion. This is the spin. So simplistically, we can say that in QM magnetic fields are not only caused by currents, but by any form of angular momentum.