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# What is hysteresis? Define the terms 'coercivity' and 'retentivity' of a ferromagnetic material.

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#### Hysteresis: The phenomenon in which the magnetic induction (→B) lags behind with respect to the magnetizing field →H is called hysteresis.It occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely.Retentivity: The property of the magnetic material to retain magnetism even in the absence of the magnetizing field is known as retentivity or remanence.Coercivity: The magnetizing field (H) needed to demagnetize the magnetic material completely is known as its coercivity.

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The figure gives experimentally measured BāH variation in a ferromagnetic material. Its retentivity, coercivity and saturation magnetization, respectively are:

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The mass of a specimen of a ferromagnetic material is 0.5 kg and its density is 8000 kg/m3. What is the energy equivalent area of hysteresis loop of alternating magnetizing field of frequency 100 Hz, if the hysteresis loss per second is 240Ć10ā3 J/s?

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