Thanks all. Overall I received the responses I expected. Undoubtedly, the
relativistic treatment is the most thorough but a little chunky for the
students to swallow so far before relativity is discussed.
I appreciate the reference to the previous thread (Bob S) and your nice
little exposition (Carl).
I didn't receive the comments I expected about the statement that the
magnetic field is responsible for doing the work on the charges. I agree
that in the frame of the B-field it looks that way. Am I just being
too sensitive over telling the students the contradictory statements
that "magnetic forces can do no work" until we get to this topic and all
of a sudden it does?
Maybe I'm just being anal --- not a first for a physicist.