Hi
I have in mind some interesting and relatively
simple experiments regarding electromagnetic induction.
The purpose is to reach a better understanding of the
very basics.

xray4abc wrote:
Hi
I have in mind some interesting and relatively
simple experiments regarding electromagnetic induction.
The purpose is to reach a better understanding of the
very basics.

How about you post your proposals here for nit picking first? I'm sure
there are a few experts here who can help get the kinks out before one
starts to build and measure.

My personal feeling is that there ought to be some relatively simple
induction experiments that could determine some definitive facts
regarding Induction, but the design of an experiment that is truly
simple and definitive takes some thought! I recall the experiments
Kelly that seemed to show that a magnetic field was attached to a
rotating magnet. They were simple, but unfortunately not definitive.
The question is still open.

Benj

OK
The first experiment I would suggest is :
Measuring the induced voltage in a horizontal metallic bar
rotating in a uniform vertical magnetic field .
Rotation would be about a vertical axis passing
through the middle of the bar.
Above and under the rotating bar should be 2 horizontal
metallic contact-rings, connected to an electrometer/voltmeter
to measure the induced voltage.
Other ideas would be : -2 ring-sectors only, connected to
an electrometer.
- no contact measurement, using the
electrically induced voltage when the 2 ends are passing near
2 given electrodes connected to the voltmeter/electrometer

This experiment is designed to - kind of - reproduce the
well known situation of a metallic bar moving in a magnetic field
as described in the classical textbooks.
I was unable to find any description of a practical experiment
of this sort in the available sources, that is why I started to think
of one myself.

Of course the rotating magnet situation could be an alternative
to this experiment.

There is then the interesting idea of the zero field.
According to this idea (I am not the author of the idea) a zero field
can
behave like the sum of 2 opposite fields. I would like to design some
experiments to test it, as I came to ideas not far from it, pondering
over the phenomenon of auto-induction.
The thing comes like with electrical charges ;one can not create
negative charges without creating corresponding positive charges.
Translated : one can not create one kind of electric field without
creating a second kind of it. This situation may apply for magnetic
fields
too.

Best regards, LL

xray4abc wrote:
OK
The first experiment I would suggest is :
Measuring the induced voltage in a horizontal metallic bar
rotating in a uniform vertical magnetic field .
Rotation would be about a vertical axis passing
through the middle of the bar.
Above and under the rotating bar should be 2 horizontal
metallic contact-rings, connected to an electrometer/voltmeter
to measure the induced voltage.
Other ideas would be : -2 ring-sectors only, connected to
an electrometer.
- no contact measurement, using the
electrically induced voltage when the 2 ends are passing near
2 given electrodes connected to the voltmeter/electrometer
This experiment is designed to - kind of - reproduce the
well known situation of a metallic bar moving in a magnetic field
as described in the classical textbooks.
I was unable to find any description of a practical experiment
of this sort in the available sources, that is why I started to think
of one myself.

IF you think about this, you find that if you measure the voltage at
the ends of the bar the emf induced in one half of the bar is balanced
by that in the other half. You really need to measure the voltage
between the center of the bar (driving rod) and the ends (circular
ring).
You are right! I got lost for a moment between the many

Of course, what you've just invented is the Faraday generator,
somewhat reduced to a simple segmented form! The bar insures that the
charges rotate with the bar which might be questioned in the disk
case. These results are well known and do indeed show the effect of a
metallic bar moving in a magnetic field.

Of course the rotating magnet situation could be an alternative
to this experiment.

Which is also of great interest to those pondering whether the
magnetic field rotates with a magnet. Here you have the cases of
rotating the magnet and keeping the bar fixed or rotating magnet and
bar together. The problem is that there is no way to distinguish the
two theories. In one case it is said that the flux does not move with
the magnet so there is no induction in the wiring. In the other case
the flux is assumed to move with the magnet but it ALSO therefore
induces a balancing emf in the wiring. As it turns out BOTH
assumptions give the same result! The question is to find a
configuration that separates the two!
Well, actually your reference to Kelly, helped me to find the

==========================

Your "zero field" question below is a VERY interesting one! The
question is do two equal and opposite fields cancel and produce NO
field or do they REMAIN separate in space and by superposition
therefore produce ACTIONS that cancel even though both fields are
present.

Here is a VERY important point with regard to the difference between
physics and mathematics. Today physicists are so enamored with math
that they accept the rules of math as reality. Zero field is the
PERFECT example. In the mathematics of vectors, two equal and opposite
vectors sum to zero. Therefore physicists conclude that when you have
equal and opposite vectors that the Field is zero. And Lo! It measures
zero on a gauss meter for example! So God is in his heaven and all's
right with the world!

But is it? Take the case of a long solenoid. If you think about it a
bit, you can convince yourself that the magnetic field contributions
from the top half of the turns is one direction while that from the
bottom half is in the other. The switching point is at the tangent
from the measurement point to the side of the coil. So do these fields
really "cancel" or do they coexist and only MEASURE zero on a
gaussmeter? The question is: Can we measure the so-called "zero
field" with some OTHER device that might show that two opposite fields
do NOT sum to a zero field? The fact that induction and quantum
effects can take place in this so-called "zero field" region may just
be the big hint that the fields are just equal and opposite and not
actually ZERO!
I picture this for myself like the

This is really fundamental stuff that I'll talk more about later.

Benj
==============



There is then the interesting idea of the zero field.
According to this idea (I am not the author of the idea) a zero field
can
behave like the sum of 2 opposite fields. I would like to design some
experiments to test it, as I came to ideas not far from it, pondering
over the phenomenon of auto-induction.
The thing comes like with electrical charges ;one can not create
negative charges without creating corresponding positive charges.
Translated : one can not create one kind of electric field without
creating a second kind of it. This situation may apply for magnetic
fields
too.

Best regards, LL- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

Well, actually your reference to Kelly, helped me to find the
description of experiments done in Ireland in 1998 to clarify this
issue.
Apparently they did answer the question: Yes, the magnetic field
does rotate with the magnet, as it supposed to do.
I am still studying their experiment, which should be repeated .

This is because, in my opinion, when a magnetic field
varies, its line-density changes ( using the field-line
representation of force-fields)
, meaning either an expansion or a
crowding of the field-lines in the considered area and its vicinity.
This, on its turn, means a movement
of the lines in space and then of course intersection with
conductors which are in space.
( For a closed circuit, the movement of lines is a sort
of radial movement)
Then, we got a case of relative motion of the conductor
versus field-lines and vice-versa.

xray4abc wrote:
This is because, in my opinion, when a magnetic field
varies, its line-density changes ( using the field-line
representation of force-fields)
, meaning either an expansion or a
crowding of the field-lines in the considered area and its vicinity.
This, on its turn, means a movement
of the lines in space and then of course intersection with
conductors which are in space.
( For a closed circuit, the movement of lines is a sort
of radial movement)
Then, we got a case of relative motion of the conductor
versus field-lines and vice-versa.

Usually people discuss two modes "flux cutting" and "flux changing"
together these two modes seem to describe phenomena. People noting
that a magnetic field about a wire stores energy and in essence must
"spin out" into space in some manner have hoped that SOMEHOW that
relative motion could be described in such a manner that these two
modes could actually BOTH be shown to be a single "flux cutting" mode.

This is actually an old idea (see Sears and Zemansky "University
Physics" 1957 edition, p 606) But he dismisses it with the words,
"There is no way of identifying one specific line of flux... The lines
of flux are a figment of the imagination, in spite of the lines we
draw to represent them and it is meaningless to speak of a line as
moving with a certain velocity."

Basically they are saying that "flux lines" are bogus and therefore
can't be used to draw any conclusions. This is true.
I contest this !

However they do
not say that the "moving field" idea cannot SOMEHOW be worked out to
generate a flux-cutting scheme. My first efforts along these lines
failed. The reason is (as we've discussed here before) that induction
works in a region of "zero B" Hence there IS supposedly no "B" moving
past the secondary conductor to induce an emf. But NOTE how this
relates to your previous discussion of "Zero B". The Question has to
be "Is there no B field in regions of zero B?" Suppose equal and
opposite B fields spin out from a toroid or solenoid. Might there not
be SOME way that those canceling fields somehow induce induction when
they have a time rate of change? That is the $64,000 question!

Benj
I think you realise, as I do, that zero-field =

By the way, you did not comment on the idea of
self-magneto-constriction ! I have imagined an
experiment to test it.