Re: is the magnetic field really moving?

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"blackhead" <larryharson@[EMAIL PROTECTED]
> wrote in message 
news:2540580d-ae9a-48b8-a909-6fdea3322c97@[EMAIL PROTECTED]
> On 15 Aug, 00:03, Christoph Kobe <christ...@[EMAIL PROTECTED]
> wrote:
>> On Thu, 14 Aug 2008 17:38:09 -0500
>> "Terry L Hewett Sr" <terrylhewet...@[EMAIL PROTECTED]
> wrote:
>>
>> > "Christoph Kobe" <christ...@[EMAIL PROTECTED]
> wrote in message
>> >news:20080814212631.3f00a56a.christoph@[EMAIL PROTECTED]
>>
>> > > I don't agree with you that there is a second field generated in
the 
>> > > iron.
>> > > Why should it be there?
>>
>> > The iron is not only conductive it is a ferrite. It will induce the 
>> > field
>> > from the wire through conductive properties carried by the field.
This 
>> > is a
>> > simple experiment wind a coil around a 1/2 inch bolt apply voltage.
see 
>> > if
>> > you don't see a second field generated by the bolt. The same would be

>> > true
>> > if you wound the coil inside of a iron pipe, however it is more 
>> > efficient to
>> > have the iron core within the coil.
>>
>> Well, the comparision (winding a wire around bolt) is really bad,
because
>> 1. The winding is not around a ferrit, it's only in a part of it. That 
>> would
>> be drilling a hole through the bolt, putting the coil through that hole

>> and only
>> around half of the bolt. The flux would be 'shortened' by the other
half 
>> of the
>> bolt, thus not generating a field outside the bolt.
>> 2. In this case there is only one winding and one winding is by far not
>> enough to cancel the other magnetic field (unless you put more than
10000 
>> A through it ...).
>> 4. We're only talking about voltage induction. No current yet. No
current 
>> means, no additional
>> magnetic field generated.
>
>> Conclusion: Theory that there is a sencond opposing field generated is 
>> wrong.
>
> When a field is applied to iron, it has the effect of aligning the
> domains - tiny bar magnets - within it so that they collectively add
> to the applied field. The effect is to intensify the total magnetic
> field within the iron, but decrease it external to the iron.
>
> Get a U magnet and add small bar magnets between the ends. The fields
> of the U magnet and that of the bar magnets add to give little
> external field but an intense field within the bar magnets.

I find your statement misleading. The field configuration will change if a

ferromagnetic material is inserted. This means that in some areas the
field 
is decreased but in others, not necessarily in the iron alone, it will be 
greatly increased. In your example the field external to the iron will be 
decreased but that is because the overall field configuration is different
- 
as you have a number of "good conductors" in parallel with the original 
"poor conductor" of the air gap. The comparison is apples to oranges
because 
the two situations are quite different.
In a motor, adding iron to the magnetic circuit greatly reduces the air
gap 
and associated mmf so that the "gap" flux is much higher than would be 
possible without the iron. Certainly "stray fields" will be reduced-that
is 
part of the purpose.   Again, it is comparing apples to oranges because
the 
overall medium and its characteristics have changed.

-- 

Don Kelly dhky@[EMAIL PROTECTED]
 the X to answer

>