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Will all the electrons in a wire will change the direction of their spin according to the magnetic field like in the picture below?

enter image description here Suppose the wire is copper

Magnetic field is coming out of the screen: enter image description here

m0Onfang
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If you have an isolated electron then it will align its spin with a magnetic field. However in a wire, as in any solid or liquid, the electron is surrounded by other electrons and their spins interact with each other as well as with any externally applied field. The end result is that the vast majority of materials respond to a field diamagnetically or paramagnetically.

In diamagnets the electrons are paired and respond very little to external fields. Paramagnets have unpaired electrons and these unpaired electrons will align with a field to some extent to give an overall magnetic dipole. However this is generally a small effect.

The other case is of course ferromagnets where there is large scale alignment leading to a large magnetic dipole, but the vast majority of materials are diamagnetic or paramagnetic.

You don't say what metal your wire is made of, but if it is copper then copper is diamagnetic so the external field will have little effect.

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John Rennie
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  • "If you have an isolated electron then it will align its spin with a magnetic field.", what about precession? – hyportnex Sep 29 '16 at 18:06