I thought I would add 3 pieces from on LH and RH from the Physics
site.
From me
The important thing is that students know that
F is normal to the plane containing I (or v) and B.

In most cases one cannot see which way current is going round the
coil producing B, so a suck it and see approach is taken, but if one
has to know one can look it up.

If we do require exam candidates to know the direction, we might as
well teach the imaginary parallel conductor method or the simple
cross product notation rather than the complicated Fleming's rule.

What is mathematically demanding?
Learning to use the right hand screw convention of the vector product
does not require going into the mathematics of vector algebra. It
would be of more use for those that go on to physics or engineering
at a higher level, it fits in with their maths for those who are
doing it, and it is be simpler for everybody including vets and
medics (who incidentally have to do biomechanics).

I first learnt about vectors (but not cross products) in 'O' level
biology (in connection with swimming sharks), long before they came
up in maths or physics.

I wonder how amused AM's students feel when they struggle to use
Fleming's rules in exams. Anything but amused I imagine!

Steve Bolter sbolter@...


-----Original Message-----
From: Physics Teaching News and Comments
[mailto:PTNC@...] On Behalf Of am
Sent: Wednesday 24 September 2003 09:22
To: PTNC@...
Subject: Re: LH and RH rules

Does this not come back to the idea of teaching to the 30,00 or the
2,400 that will continue with physics at University.

Making the course more mathematically demanding may well improve the
standard of the 2,400 passing through to undergraduate level but will
no doubt reduce the number choosing A level physics because of the
extra mathematical content. This would be backtracking on much of
the work done recently to improve the subject's popularity. It has
certainly been a while since A level mathematics was seen as
essential for the study of A level Physics. We may end up losing
those medics/vets etc that choose Chem, Phys, Biol?

Perhaps a better solution would either for individual schools to
teach beyond the specification to the more able or perhaps to lobby
for a mathematical optional topic?

My experience has been so far that students find these memory aids
useful and quite fun. I certainly find it amusing to see them try it
during tests/exams!

Adrian Meadows.

From sbolter@...
I have never been able to use the Fleming's LH and RH rules.
1 I cannot remember which hand to use for which effect;
2 I cannot remember which finger and thumbs are which;
3 there are two different ways in which I can put my thumb
and first two fingers in mutually perpendicular directions.

There is no virtue in these rules. They add nothing to understanding
and are exceedingly difficult to remember and use. The ability to use
them (or other memory aids unrelated to the principles involved) DOES
NOT in general indicate they UNDERSTAND - much research shows this to
be the case.

What is the point of learning such one off rules, when one can learn
to use vector (and scalar) products which are applicable in so many
situations in A level and beyond?

I did not know that vector products have been taken out of the A
level maths syllabuses. Even if they have, it is worth putting vector
products in as a mathematical requirement for Physics, because it
makes the expression of three dimensional effects so much simpler. It
is mad to deny physics students mathematics that was designed to make
physics simpler; just as it is mad not to use physical examples when
teaching the mathematics.

It is child's play to work out the direction of the force if one uses
F
= Q v × B without any fingers or thumbs, and it is simpler to learn
whether it is v × B or B × v, than it is to learn all those fingers
and thumbs, the correct hand and the correct posture.

However there are ways to get the directions correct without using
cross products or LH or RH rules, neither of which develop
understanding.

For the force on a current carrying conductor in a magnetic field one
needs to know the corkscrew rule - something that one has to know
anyway, and that like currents attract / opposite current repel,
something that is a standard demonstration. Simply imagine/draw a
parallel conductor. Use the corkscrew rule to work out the way a
current in the new conductor would have to flow to be the source of
the field (or relevant component) and then put in repulsive or
attractive forces as appropriate. This way relates to other topics
and develops an overview that aids understanding.

For the direction of the e.m.f. induced in a conductor, one only has
to imagine it to be the fourth side of a frame with three fixed sides
and use Le Chatelier's Principal / Lenzes Law (sorry, but if I
pronounce the e, I do not put an apostrophe instead) / conservation
of energy to deduce the direction of the induced current. Again this
aids understanding, which the RH rule does not. (No I did not
remember. I looked up that it was RH)

The only reason to do RH and LH rules is that they can be asked for
in exams. There has been an A level exam which specifically required
Fleming's rule to get the marks. It was wrong to ask for this. Any
way of correctly finding the direction should have been accepted.

Steve Bolter sbolter@...


> >
> >-----Original Message-----
> >From: Physics Teaching News and Comments
> >[mailto:PTNC@N...]On Behalf Of Gren Ireson
> >Sent: 23 September 2003 13:39
> >To: PTNC@N...
> >Subject: Re: LH and RH rules
> >
> >
> >Not as easy as it appears this!
> >
> >Why do we bother to teach ... seems a rather strong term and could
be
> >applied to so much physics; why bother to teach the Bohr model of
the atom
> >and a model based on charge probability density?, why bother to
teach a
> >version of the Dirac Sea model for anti-matter which can't be used
with
> >bosons and not the Klein-Gordon equation?, Why bother with a
study of
> >electromagnetism other than one which includes Maxwell's equations?
> >
> >Of the 30 000 ish physics A-level students only about 2400 go on
to an
> >undergraduate course in physics and hence I would argue that:
> >
> >1. school physics at GCSE and A-level should be accessible to the
30 000
> >(and no A-level spec includes cross-products, or dot-products, in
its
> >mathematical requirements - perhaps the development groups thought
this
> >through) where the LH and RH rules do allow the students to make
predictions
> >regarding physical phenomena.
> >
> >2. university students do not need to 'unlearn' school physics but
rather to
> >be shown how their current understanding can be extended to
include a more
> >sophisticated (and often more mathematical description).
> >
> >3. knowledge of vector and/or scalar products (or other
mathematical
> >devices) by students and the ability to solve numerical problems
using them
> >DOES NOT in general indicate they UNDERSTAND - much research shows
this to
> >be the case.
> >
> >Gren
> >
> >"If we want things to stay as they are, things will have to change"
> >(Di Lampedusa, The Leopard, 1957)
> >
> >Dr Gren Ireson CPhys MInstP ILTM
> >Matthew Arnold Building
> >Loughborough University
> >Leicestershire
> >LE11 3TU
> >UK
> >
> >+44(0)1509 222784
> >----- Original Message -----
> >From: "Elizabeth Parvin" <emp4@T...>
> >To: <PTNC@N...>
> >Sent: Tuesday, September 23, 2003 12:24 PM
> >Subject: Re: LH and RH rules
> >
> >
> > > Speaking from the university point of view, I could not agree
more. One of
> > > the first things we have to do for new undergraduates is
to 'unteach' all
> > > the stuff about RH and LH rules and teach vector cross
products and the
> >> right hand rule. Everything can be done using the one rule then.
> >>
> >> Liz Parvin
> >> Warwick University
> >>
> >>
> >>
> >> PTNC@N... writes:
> >> >Can someone explain : why do schools bother with LH and RH
rules for
> >> >motors and generators. Why not use a simple RH coordinate
system rule
> >> >throughout, F = qv x B (as in z = x cross y) : F is the first
finger, v
> >> >is the second finger and B is the thumb.
> >>
>
>
> --
>
> Dr. Keith S. Taber
> http://www.educ.cam.ac.uk/staff/taber.html
> University Lecturer in Education
> University of Cambridge Faculty of Education
> Homerton College site
> Hills Road
> Cambridge CB2 2PH
>
>
> to join an electronic discussion list on
> learning in science
> please visit
> http://uk.groups.yahoo.com/group/learning-science-concepts