force on conductor carrying currentsurrounded by solid magnetic material

djsourabh

i want to compare force on current carrying conductor ,
1)placed in air surrounded by magnetic field
2)placed in the cylindrical cavity(without air gap but some electrical insulation) which is placed in magnetic field.
please give me practically calculated answers with calculations.

berkeman

Well, do you know the equation to use for your case #1? It's a common equation:

http://hyperphysics.phy-astr.gsu.edu...c/forwir2.html

And for your case #2, could you maybe clarify a bit about the geometry? Is there some application that you have in mind? I think I know the answer, but need a few more details before commenting about the force for case #2...

djsourabh

i meant ,how much times is the force for case 2 that of case 1?

berkeman

Negative infinity (or zero, depending on how you write the fraction) most likely. But that's why I asked for more information about the configuration of case #2. Can you provided a sketch?

What is the context of your question? Is it a thought experiment, something for schoolwork, or somthing that you want to build and test?

djsourabh

i want to build & test it.
can you provide mathematical or logical explanation for your answer ?
take sketch as
there are 2 poles of magnet separated by a distance.in between them space is filled by magnetic material .
it contains cavity having conductor carrying current.
can you give me the formula and practical answer for above scenario?
what are values of relative permeabilities for magnetic materials?

berkeman

(Please do not use text speak like "u" and "ur" here on the PF. It is against the rules. I have fixed up your post above).

The cavity in the magnetic material is shielded from the external B-field. That's what magnetic materials do -- they concentrate and divert magnetic fields. So the wire in the cavity will experience very little or zero magnetic field, and there will be a correspondingly small force on it.

ZenonDorin

My new electric motor is based on exactly this thing (part of the coil is in the cavity of a permalloy).

http://www.physicsforums.com/showthread.php?t=663657

berkeman

I skimmed the video, but was not able to quite understand what is going on (I'm at work and cannot spend much time viewing it). Is there supposed to be audio that goes with the video?

But if you have permalloy surrounding some of your wires, they will not have much force applied to them because of the shielding effect.

ZenonDorin

Yes, you cannot understand without audio.

That's the key. On a certain portion there must be no electromagnetic force, else the integral of force on the entire coil would be 0.

No matter how you place the magnet or the coil, without such shielding or without current switching (with an electronic speed controller or brushes), there can't be any continuous rotation which is required in an electric motor.

djsourabh

so, in which material medium the force on current carrying conductor will be highest?
(consider above configuration)