The area of hysteresis loss is a measure of

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Energy loss per cycle

Explanation: The area enclosed by the B-H hysteresis loop of a magnetic material represents the energy dissipated as heat within the material during one complete magnetization cycle. This energy loss is a direct consequence of the irreversible movement of magnetic domains when subjected to an alternating magnetic field.

Working Principle: When a ferromagnetic material is exposed to an alternating magnetic field, its magnetic domains must rotate or reorient to align with the field. This movement encounters internal friction, causing some energy to be dissipated as thermal energy. The total energy lost per unit volume per cycle is given by the integral of H with respect to B, which geometrically equates to the loop area.

Key Formulas: $W_h = \oint H \cdot dB$ — Energy loss per unit volume per cycle, representing the loop area

Key Points: Hysteresis loss depends on the area of the B-H loop and the frequency of the alternating field.; Materials with small hysteresis loops (narrow area) are termed 'soft' magnetic materials and are ideal for transformer cores.; Hard magnetic materials exhibit large hysteresis loops and are used for permanent magnets.; Steinmetz's empirical formula relates hysteresis loss to the maximum flux density: $P_h = \eta B_{max}^{1.6} f V$.

Advantages: High loop area is beneficial for permanent magnet manufacturing.; Low loop area minimizes energy waste in electrical machinery.

Disadvantages: Hysteresis loss leads to unwanted heating in electromagnetic devices.; Reduces the overall efficiency of power transformers and rotating machines.

Applications: Transformer cores; Electric motor armatures; Permanent magnet design

Additional Info: The SI unit for energy loss per unit volume is Joules per cubic meter ($J/m^3$).. Permeability is the slope of the B-H curve ($B = \mu H$), not the area.. Permittivity relates to dielectric materials and electric fields, not magnetic hysteresis.

Answer: B is correct — The area of the hysteresis loop corresponds exactly to the energy dissipated as heat during one full magnetic cycle.

Exam Tip: Always remember that hysteresis loss increases linearly with frequency ($f$), so high-frequency applications require materials with extremely narrow hysteresis loops to prevent overheating.

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