Motion of wire in B field -vs- motion of electrons in helmholtz coils

[motorman]

Hi guys,

This may be a daft question (or set of questions), but I just want to bounce a few ideas off the wall once I understand some simple issues.

Can anyone tell me why if you pass a current through a wire in a magnetic field, the wire will move perpendicular to the both the current and field.

Yet, if you fire an electron beam into chamber with helmhotlz coils providing the field the electrons try to curl/deflect from their path?

Shouldn't the wire and and electron beam behave in the same manner?

And more fundamentally, why is there quadrature in the example of the wire? What goes on at the atomic scale?

Cheers

 

[technician]

As you point out, a current carrying wire experiences a force in a magnetic field.
The electrons flowing in the wire experience the force but because they are confined to the wire the wire as a whole experiences the force.
Moving Free electrons in a vacuum tube will also experience the force but these electrons are not confined to a wire so they are deflected into curved paths.
The electrons in a wire do get deflected in the wire and a voltage is produced called the Hall voltage. This effect is called the Hall effect

 

[motorman]

Thanks for the reply.

So if the electron beam starts to curl in a field, would it mean that the wire (or the current in the wire) tend to curl too? what experiments have been done to prove/disprove this?

Would the wire twist perhaps?

 

[technician]

I think that the 'curl' you are referring to is the sideways deflection of the electron flow along the wire.
The only thing that I can relate this to is the generation of an emf across the wire at 90 degrees to the direction of the current. This is the Hall effect.