Re: Magnetic N and S poles

["John S. Denker" <jsd@MONMOUTH.COM>]

Ludwik Kowalski wrote:
> I suspect that no introductory textbook published before 1945
> defined B in terms of  Lorentz formula. But I may be wrong.

I would be surprised and disappointed if _any_ textbook,
introductory or otherwise, pre-1945 or otherwise, defined
B in terms of the Lorentz force law.  By the same token
I would be surprised and disappointed if _any_ textbook
defined B in terms of N and S poles.

I am trying to imagine a homework question or quiz question:
  Fill in the blank:
    By definition, the magnetic field is __________ .

I can barely imagine answering such a question at all.
Certainly the answer cannot be anything so simple as
force per unit velocity per unit charge, or anything
like that.

I can imagine giving a list of "characteristic properties".
If I stretch and struggle I can imagine somebody calling
them "defining  properties" provided nobody takes it too
seriously.

The main point remains, as I have said before:  The whole
thread strikes me as misguided.  In high-school geometry,
there are certain things (point, straight line, ...) that
are _not_ defined.  They are abstractions.  Whatever
meaning they have comes not from their definitions, but
from the way they are used to define other things.

To put things in more positive terms, consider the
following quiz questions:
  Fill in the blanks:
   1) Some of the important properties of the
   magnetic field are: _____________________,
   _________________________________________,
   _____________________________________, and
   _________________________________________.
   2) Three different good ways of measuring
   the magnetic field include: ____________,
   ____________________________________, and
   ________________________________________.

Or make a true/false version of it, or a multiple
choice version of it, to make it easier to grade.

I really think it is misguided for the teacher to ask
for "the definition" of the magnetic field.  If the
student asks for a definition, suggest a better question,
such as "what are some good ways to measure a magnetic
field".