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Magnetic Field Intensity | Definition Formula

Magnetomotive force, ℑ , per unit length, is called the magnetic field intensity H.

Magnetic Field Intensity Unit

Magnetic field intensity is also known as the magnetizing force which is measured is ampere-turns per meter (A-t/m).

Of primary concern, however, is the magnetomotive force needed to establish a certain flux density, B in a unit length of the magnetic circuit.

Magnetic Field Intensity Formula

The letter symbol for magnetizing force (magnetic field intensity) is H. The following relationship defines H as;



      ℑ =applied MMF in ampere-turns

      l =average length of the magnetic path in meters


Find the magnetic field intensity in the magnetic circuit shown below:


We can calculate the intensity using following formula:



If the dimensions of the magnetic path were changed, the value of H would also change. Fox example, if the total length of the magnetic path doubled, we should expect the value of H to decrease to one-half its previous amount.

If physical dimensions are double for the above circuit, then magnetizing force will be;


So, we can observe that, for a given number of ampere-turns, the magnetizing force varies inversely per unit length of the magnetic path.

About Ahmad Faizan

Mr. Ahmed Faizan Sheikh, M.Sc. (USA), Research Fellow (USA), a member of IEEE & CIGRE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from Kansas State University, USA.

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