Electrical Engineering ⇒ Topic : Magnetic Field Intensity

MAGNETIC FIELD INTENSITY

The ratio of magnetomotive force per unit length of the magnetic flux path is called magnetic field intensity. Its symbol is H.

                                                                               .............. (1)

where L is the mean length of the magnetic circuit in metres. Magnetic field intensity is also called as magnetic field strength or magnetizing force.

From Eq. (1),

                                                                                                    .................. (2)

   Magnetic intensity (or field strength) at a point in a magnetic field is the force acting on a unit N-pole (i.e., N-pole of 1 Wb) placed at that point. Clearly, the unit of H will be N/Wb.

Suppose it is desired to find the magnetic intensity at a point m - P situated at a distance d metres from a pole of strength m webers (See Figure (A). Imagine a unit north pole (i.e. N-pole of 1 Wb) is placed at P. Then, by definition, magnetic intensity at P is the force acting on the unit N-pole placed at P i.e. Figure.

Magnetic intensity at P, H = Force on unit N-pole placed at P  

                                     FIGURE  (A)

The reader may note the following points carefully

• Magnetic intensity is a vector quantity, possessing both magnitude and direction. In vector form, it is given by

• If a pole of m Wb is placed in a uniform magnetic field of strength H newtons/Wb, then force acting on the pole, F = m H newtons.