Is the Magnetic Force Really Doing No Work?

[cabraham]

I disagree with the part highlighted in red. The upward force on an electron, due to its orbital motion, in an external magnetic field must come from the horizontal component of the field. However, electrons (and atoms) also have an intrinsic dipole moment, and an entirely vertical field can still produce an upward force on them as a result. Close to a large (in comparison to the object being lifted) magnet, the vertical component of the field is much larger than its horizontal components (when you are more or less centered below one of its poles). Moreover, the intrinsic magnetic moments of atoms are often much larger than the dipole moments due to the orbital motion of their electrons. When you lift iron filings, or a car, using a magnetic field, the vertical component of the field is usually the dominant factor.

We are really talking about dipoles for the crane/car example of Studiot's (Intrinsic dipole moments (spin) are the dominant source of Ferromagnetism)--- or when lifting iron filings with a fridge magnet. As far as I can tell, Studiot's main issue at this point is how, according to the Lorentz force law, the force on a dipole can be parallel to the applied magnetic field. This is the issue I think your earlier argument was failing to address. I think you were sidestepping the issue by claiming that the horizontal components of the field were responsible.

I was not sidestepping any issue. Of course the dipole moments are important, I never denied that. The question I was addressing was how on Earth can a z-oriented B field lift an e- vertically. I was just pointing out that there is some component of B in the lateral x-y plane. The Lorentz force law involving v x B does not fail for individual e- as long as we account for thr lateral B component. That was my point.

I am well aware that orbiting e- & moving charges in general have an associated magnetic dipole moment. That has never been disputed. If you examine the moments involved you can ascertain the upward lift force. I was only demonstrating that the Lorentz law is still valid when viewing an individual e-. Some inferred that modern science cannot explain the upward lift, & that Lorentz' law was invalid, & I just addressed that issue to show that it is valid.

I don't have any beef w/ your magnetic moment discussion at all.

Claude

 

[gabbagabbahey]

The question I was addressing was how on Earth can a z-oriented B field lift an e- vertically. I was just pointing out that there is some component of B in the lateral x-y plane. The Lorentz force law involving v x B does not fail for individual e- as long as we account for thr lateral B component. That was my point.

And I feel this argument is misleading. In many cases, the horizontal components of the (external) field contributes very little to the lifting power of a magnet, and hence are often negligible (Like in the crane/car experiment). This doesn't mean that you can't apply the Lorentz force law and end up with a net vertical force from an entirely vertical field. The equation for the force on a dipole can be easily derived directly from the Lorentz force law. As can the equation for the force on a magnetizable material.

 

[UWStudent101]

Would anyone be able to give me an explanation of the magnetic forces regarding physically how they work? It is their physical property that I find fascinating rather than their equations and vector solutions. Any theories or explanations would be appreciated.

 

[quantum123]

Very interesting stuff. I happened to get an email notification and then start reading this thread. Thanks to you guys for the thought provoking discussion using various angles to look at this phenomenon, which is still rather mysterious to me.