Re: First Law (now perpetual motion)

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Sun, 24 Jan 1999 20:28:14 -0600 Herb Schulz <herbs@INTERACCESS.COM>
writes:
> At 10:28 AM -0500 on 1/24/99, Herbert H Gottlieb wrote:
> > I know that it won't work, but I wonder if your explanation of WHY
> it won't work is correct....... .......????
> > If we connect a long wire to the terminals of a galvanometer and
> then move a small section of this wire between the poles of a horseshoe
> > magnet, the wire cuts magnetic lines of force and induces a current in
the
> > galvanometer. Similarly, if a small section of a wire is stretched from
wingtip to
> > wingtip of an airplane and the rest of the wire is covered by magnetic
> shielding, we should have the changing flux through the loop that you
say is
> > necessary.
> >
> > Herb Gottlieb from New York City
> > (Where the earth's magnetic flux lines are essentially vertical)
>
> Howdy,
>
> Notice that I didn't say anything about "cutting magnetic lines of
> force." I said that there must be a changing flux through the loop.
Pulling
> one part of the loop through a region with a non-uniform B-Field will
> change the number of magnetic lines that pass through the enclosed area
of
> the loop, i.e., change the magnetic flux through the loop.
>
> I've also gotten to dislike Electric and Magnetic Field Lines being
> called Lines of Force.  Students begin to think that there is a force on
a
> point in space which couldn't be further from the truth.  There will be
a
> force on a charged particle placed at some point in space (if E isn't
zero
> at that point) or on a charged particle moving through a point in space
> (if B isn't zero at that point) but there is nor force at or on the
point
> itself.


When a portion of a horizontal conducting loop first enters a vertical
magnetic field
(whether or not the field is uniform)  a current is induced in the loop
and the
loop experiences a real force. Although we do not believe that there are
actually magnetic lines of force in the field, the concept of these lines
helps students to visualize the electromagnetic effects that we observe.

Herb Gottlieb from New York City
(Where we truly believe in lines of force ...and Santa Clause too)