Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Force on a charged particle from a magnetic field



Despite John Denker's willingness to consider agreeing with the spirit of my comments about Maxwell's equations being, in principle, adequate to answer Bob LaMontagne's original question because they have relativity "built into them," I think he's giving me too much credit. Although it is true that the Lorentz transformations are in some sense mandated by Maxwell's equations, that was not what I had in mind. I have learned something from reading the responses that remark generated and stand corrected.

But with that mea culpa out of the way, I would like to register my disagreement with Jack's and Bob's suggestion that we stay away from this example in an introductory course. In my opinion, the moment we introduce the Lorentz force, we become almost obliged to point out the seeming absurdity of a force that depends on velocity--not *relative* velocity, just velocity--and that vanishes in the frame of the moving particle. It is not asking too much of students to ask them to appreciate that an immediate implication of that fact is that the electromagnetic field is frame-dependent.

By all means, leave the details to a later course. But why not plant the seeds of understanding early. We all know how much more effective it is to return to a topic than to see it for the first time.

John Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://outlawsofphysics.com>