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.

 

[sardar]

There are a few key differences between the motion of a wire in a magnetic field and the motion of electrons in Helmholtz coils. Let's break down each component to understand why they behave differently.

First, let's look at the wire. When a current is passed through a wire, it creates a magnetic field around the wire. This magnetic field interacts with the external magnetic field, causing the wire to experience a force perpendicular to both the current and the field. This is known as the Lorentz force and is described by the equation F = I * L * B, where I is the current, L is the length of the wire, and B is the external magnetic field. This force causes the wire to move in a circular path, perpendicular to both the current and the field.

On the other hand, in the case of the electron beam in Helmholtz coils, the electrons are not creating their own magnetic field. They are simply being affected by the external magnetic field created by the coils. This field causes the electrons to experience a force known as the Lorentz force, which is described by the equation F = q * v * B, where q is the charge of the electron, v is its velocity, and B is the external magnetic field. This force causes the electrons to deflect from their original path, resulting in a curved trajectory.

So, the main difference between the wire and the electron beam is that the wire is creating its own magnetic field, while the electrons are only being affected by an external field. This leads to different types of forces acting on each and therefore different types of motion.

As for the quadrature in the wire example, this is due to the way the Lorentz force is acting on the wire. This force is always perpendicular to both the current and the field, resulting in the wire moving in a circular path. At the atomic scale, the same principles apply. The movement of individual charged particles in a magnetic field is governed by the Lorentz force, which results in circular motion.

I hope this helps to clarify the differences in motion between a wire and electrons in Helmholtz coils. Keep asking questions and exploring these concepts, as they are important in understanding the interactions between electricity and magnetism.