What is the source of magnetism in matter? A rod made of a ferromagnetic materia

Question

What is the source of magnetism in matter?

A rod made of a ferromagnetic material characterized by the hysteresis loop shown in the figure below. If the rod is 50 cm long, with a circular cross-section, 1 cm2 in area:

(i) Calculate the pole strength of the rod after being magnetized to saturation and removed from the magnetizing field.

(ii) Calculate the magnetic field intensity of the rod at a point in line with the rod 50 cm from its nearest end.

excellent solutions = rate

Explanation / Answer

Magnetism arises from two sources -- Electric current andSpin magnetic moments of atoms or nuclei. The magnetic moments of the nuclei of atoms are typically thousands of times smaller than the electrons' magnetic moments. Nuclear magnetic moments are nevertheless very important in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).

(i) pole strength p = MA, where M is magnetization and A is the cross sectional area. M = ~4.5J (from the curve at saturation)

=> p = 4.5 J * 10-4 = 4.5×10-4 J m2

(ii) Magnetic field is defined as B = p[ ( z-l/2)/r13 - (z+l/2)/r23 ]

z = 50+25=75 cm, r1 = 50cm, r2 = 50+50=100cm, l = 50cm, p = 4.5×10-4 J m2

B = 4.5×10-4 ( (0.75-0.25)/0.503 - (0.75+0.25)/0.1003 ) = - 0.448 T

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