# Calculate Magnetic Field of Electromagnet with Hollow-Iron Core

• cb767
In summary: CalebIn summary, the conversation is about constructing an electromagnet with a hollow iron core and finding the formula to calculate the magnetic field of the electromagnet. The participants have tried searching online and in textbooks but have found nothing. They discuss the distribution of the magnetic field and mention different software that could help with simulations. They also mention the need for validation of their understanding and ask for thoughts and equations related to air core electromagnetic coils.
cb767
Hey everyone,

I'm doing a physics project, and I need to construct an electromagnet with a hollow iron core. I have searched everywhere on google, and checked my physics textbook as well, but have unfortunately found nothing. I basically just need the formula of how to calculate the magnetic field of an electromagnet, which has an iron-cylinder core.

Thanks,
Caleb

I am dying to know that too...!

I have the same configuration ...i.e. a coil wound round a iron tube .I want to know the field inside the tube.Having a core complicates the matter...

For a hollow iron tube without windings inside the tube, what tangential component of the magnetic field is continuous across the air-iron boundary? Why?

Sorry,Bob S I did'nt exactly understand your question...

There are no coils inside the tube.The coil is outside the tube.It is made by winding a magnet wire on a soft iron tube...simple.

Actually what I have found so far is that there are standard formulas for air core electromagnetic coils.So we get a more or less uniform field within the coil.there is small radial variation and axiially i.e. along the height of the coil the field at the middle is maximum and at the two ands (top and bottom)half of the maximum.

Now, as I add a hollow cylindrical soft iron core (a soft iron tube)almost all the flux lines go through the iron tube thus in effect screening the inside and so the inside of the tube is starved of magnetic flux.The field will be very high at the top of the tube wall as it is now turned into a magnet due its magnetization and north pole and south pole will be formed at the two ends(it also formed for a air core solenoid but the strength would be weak)just at the top of the tube wall.Hope I didn't mess up the explanation...

This is all fine and validated.I want exact field values at arbitrary points in 3d space both inside the tube and out side the tube i.e the 3d field distribution of B and H.

I know couple of solvers (simulators)which can be of some help but I need someone to accompany me by sharing their results of the simulation of the configuration in prder to validate my understanding.
...
1.FEMM...excellent...so far the best and lightweight field solver I have ever encountered.Its open source software so ..FREE DOWNLOAD!
this is the homepage:
http://femm.foster-miller.net/wiki/HomePage
2.Maxwell SV:
3.VIZIMAG small software ,lacks in flexibility to model complex geometries.
4.quickfield
5.comsolOr one can try and solve MAXWELL equations in the 3d (or 2d)space to get the field distribution...

Thanks to all.

We agree. There are no coils inside the tube. So Curl H = 0. Solve it at the boundary. So what tangential component of the magnetic field is continuous across the boundary on the inside of the iron tube? What tangential component of the field is NOT continuous?

cb767 said:
Hey everyone,

I'm doing a physics project, and I need to construct an electromagnet with a hollow iron core. I have searched everywhere on google, and checked my physics textbook as well, but have unfortunately found nothing. I basically just need the formula of how to calculate the magnetic field of an electromagnet, which has an iron-cylinder core.

Thanks,
Caleb

I want to know that too :) created a post too just to find this 1 out.

I am trying to find the solution to that exact construction.

Hi Souviktor, I read your reply to Bob S. In that you said that there are standard formulas for air core electromagnetic coils. I am now searching for that equation for my project. It will be helpful to me if you provide me that equation.

Thanks

## 1. How do you calculate the magnetic field of an electromagnet?

The magnetic field of an electromagnet can be calculated using the formula B = μ₀ * N * I / L, where B is the magnetic field, μ₀ is the permeability of vacuum, N is the number of turns in the coil, I is the current in the coil, and L is the length of the coil.

## 2. What is the role of the hollow-iron core in calculating the magnetic field of an electromagnet?

The hollow-iron core is used to increase the strength of the magnetic field produced by the electromagnet. It helps to concentrate the magnetic field lines, making it stronger and more effective.

## 3. How does the number of turns in the coil affect the magnetic field of an electromagnet?

The number of turns in the coil directly affects the strength of the magnetic field produced by the electromagnet. The more turns in the coil, the stronger the magnetic field will be.

## 4. Can the magnetic field of an electromagnet be changed?

Yes, the magnetic field of an electromagnet can be changed by adjusting the current in the coil or by changing the number of turns in the coil. Increasing the current or number of turns will increase the magnetic field, while decreasing them will decrease the magnetic field.

## 5. How does the length of the coil impact the magnetic field of an electromagnet?

The length of the coil also affects the magnetic field of an electromagnet. A longer coil will produce a stronger magnetic field compared to a shorter coil. This is because a longer coil has more surface area for the magnetic field lines to pass through, resulting in a higher strength.

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