Out of the following materials, the area of hysteresis loop will be least for………

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Examoogle · Accepted Answer

silicon steel

Explanation: The hysteresis loop area represents the energy dissipated as heat per unit volume during one cycle of magnetization. Silicon steel exhibits a very narrow hysteresis loop, resulting in minimal magnetic energy loss, which makes it ideal for transformer cores and electrical machines.

Working Principle: The energy loss per cycle is directly proportional to the area of the B-H curve, given by the Steinmetz hysteresis loss formula $W_h = \eta B_{max}^{x} f V$. By adding silicon to steel, the material's magnetic retentivity and coercivity are reduced, thereby 'shrinking' the loop width and lowering the energy waste.

Key Formulas: $W_h = \eta B_{max}^{1.6} f V$ — Steinmetz hysteresis loss formula where $W_h$ is energy loss, $f$ is frequency, and $V$ is volume.; $Area = \oint H dB$ — The physical definition of the area under the B-H loop as energy density per cycle.

Key Points: Hysteresis loss is directly proportional to the area of the B-H loop.; Hard steel is a magnetically hard material with a large hysteresis loop, making it suitable for permanent magnets.; Silicon steel is magnetically soft, providing low core loss (iron loss).; Adding silicon increases electrical resistivity, further reducing eddy current losses in addition to hysteresis losses.

Advantages: Lower heat generation in transformers; Improved energy efficiency of electrical machines

Disadvantages: Silicon steel is more brittle than mild steel; Increased manufacturing complexity

Applications: Transformer cores; Stator and rotor laminations for motors and generators

Additional Info: Silicon steel typically contains 1% to 4.5% silicon.. Hard steel has a very wide loop, representing high coercivity and retentivity, which is the opposite of the requirement for low-loss electrical machinery.

Answer: B is correct — Silicon steel has the least hysteresis loop area among the options, minimizing energy dissipation during magnetic reversal.

Exam Tip: Always remember that 'magnetically soft' materials have thin hysteresis loops (low loss), while 'magnetically hard' materials have wide loops (permanent magnets).

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