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848_Physics ProblemsTechnical Physics

848_Physics ProblemsTechnical Physics - 188 Sources of the...

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188 Sources of the Magnetic Field Q30.25 A “hard” ferromagnetic material requires much more energy per molecule than a “soft” ferromagnetic material to change the orientation of the magnetic dipole moments. This way, a hard ferromagnetic material is more likely to retain its magnetization than a soft ferromagnetic material. Q30.26 The medium for any magnetic recording should be a hard ferromagnetic substance, so that thermal vibrations and stray magnetic fields will not rapidly erase the information. Q30.27 If a soft ferromagnetic substance were used, then the magnet would not be “permanent.” Any significant shock, a heating/cooling cycle, or just rotating the magnet in the Earth’s magnetic field would decrease the overall magnetization by randomly aligning some of the magnetic dipole moments. Q30.28 You can expect a magnetic tape to be weakly attracted to a magnet. Before you erase the information on the tape, the net magnetization of a macroscopic section of the tape would be nearly zero, as the
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