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# Electrical Engineering/Calculating magnetic field strength of a C core electromagnet

Question

C Core electromagnet
QUESTION: Hi Cleggsan,

I hope this message finds you well.
I am interested in calculating the magnetic field of a C core electromagnet and I was wondering if you could tell me whether the formulas I am using are applicable in this situation.
On the Wikipedia page for electromagnets ( http://en.wikipedia.org/wiki/Electromagnet ) under the heading "Magnetic field created by a current" I have found two formulas which I put in the attached image. (I had to change one of them to suit my line of enquiry) Could you tell me if I am using the correct formulas here? I think they are appropriate, but I am not completely certain.
Am I measuring the length of the core and the length of the gap correctly?

As always, I appreciate your suggestions!

I hope all is well with you. Arigato gozaimasu
Eddie

ANSWER: Yes, all is well.

You are a very persistent person.

Yes, I believe the equations in the jpg image are correct but only for a C core.

If the configuration of your core on which the coils are wound are not in the shape of a C then you need to look for an equation suitable for your core configuration.

Domo.

[an error occurred while processing this directive]---------- FOLLOW-UP ----------

electromagnet core are
QUESTION: Thanks Cleggsan,
I am now trying to calculate the force in Newtons that the horseshoe core electromagnet will generate. Not an easy thing to do, but I am trying to start somewhere.
I want to position a permanent magnet above one of the horseshoe electromagnet's poles(contained in a tube so it can't spin around), where it may move up and down when repelled or attracted by the electromagnet.
I have found a formula on the page http://en.wikipedia.org/wiki/Electromagnet under the heading "Force Exerted by the magnetic field", where is says the "The force exerted by an electromagnet on a section of core material is:
F = (B squared*A)/(2*μ0)

Where
F = force exerted by magnetic field in Newtons
B = Magnetic field (magnetic flux density) in Tesla
A = Cross sectional area of core in square meters
μ0 = free space permeability

My question is related to the Cross sectional area of core. As far as I can tell, the thicker the core, the more force. In an attempt to increase the force generated, can I make one pole thicker than the other? (The thin pole has a space limitation)
If this would work, can I take the average of the Cross sectional area of the two poles and use this number as the A value in the equation?

Itsumo arigato Cleggsan. Sorry if it turns out I am talking crazy/ignorant!

Best regards,
Eddie

Seems to me you are on the right track.

I think of the equations for computing field strength and such as approximations because in reality the physical shape is different for each trial, the nearby fields may effect the outcome, the materials used always are uncertain, etc.  The design engineers always use final testing for verification of the design equations.

But the coil form described in the url you mentioned is for a C-I configuration (which has a bar across the ends of the C form.

And, if the core is laminated that would make a big difference as well.

Keep plowing on!

Electrical Engineering

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#### cleggsan

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