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

["Krishna Chowdary" <professor.head@gmail.com>]

On 11/28/06, Bob LaMontagne <rlamont@postoffice.providence.edu> wrote:
> But my question is how we justify the answer to this narrowly posed
> question
> in terms of the E&M available in an introductory physics course. Where
> does
> the electric field that the (assumed stationary) proton experiences come
> from since there is no time varying magnetic flux from a uniform field?


As pointed out, it has to be transformations of fields due to frame
shifting.  Electric fields by themselves are not invariant.  Magnetic fields
by themselves are not invariant.  But some combination of electric and
magnetic fields is invariant.


Is an appeal to a relativistic transform of the field tensor the only
> answer? Is it correct that Maxwell's equations alone, with no appeal to
> relativity, cannot answer the question?
I think that the answer to these questions is yes.  I've seen people mangle
Faraday's Law to get the "correct" answer, but as you point out in your
original message, that won't work.  The correct description requires
relativity.

I think that this is a nice way to introduce special relativity.  As Skip
points out, we should give credit to Einstein.


--
regards
-Krishna