Introduction / Context:
Magnetic hysteresis refers to the lag of magnetic flux density (B) behind magnetizing force (H) during cyclic magnetization of ferromagnetic materials. The area of the B–H loop represents energy loss per cycle, which becomes prominent when the excitation changes with time. Recognizing when hysteresis becomes most evident is key for transformer, inductor, and motor design.
Given Data / Assumptions:
- Ferromagnetic core excited by a coil.
- Sinusoidal or varying current that produces a time-varying H.
- Loss mechanisms include hysteresis and eddy currents (distinct phenomena).
Concept / Approach:
- Hysteresis loss per second ≈ (loop area) * (excitation frequency); more cycles per second → more total loss and more obvious effect.
- At steady DC (no change), there is no repeated loop traversal; hysteresis manifestation diminishes.
- Saturation is a separate nonlinear effect; while it affects magnetization, it is not the definition of hysteresis visibility.
Step-by-Step Reasoning:
When current changes frequently, the B–H trajectory loops continuously, incurring energy loss each cycle.These losses convert to heat and can dominate core behavior at higher frequencies.Therefore, hysteresis is most apparent under frequently changing magnetization (AC conditions), not steady DC.
Verification / Alternative check:
Design charts specify hysteresis loss ∝ f for a given material and flux swing; measurements confirm higher loss at higher frequencies.
Why Other Options Are Wrong:
- Flux not confined to the core: That describes leakage flux, not hysteresis.
- Steady DC current: No cycling; minimal hysteresis manifestation.
- Core saturation: Nonlinearity issue; not synonymous with hysteresis dominance.
- None of the above: Incorrect because frequent current change is the correct condition.
Common Pitfalls:
- Confusing eddy-current losses (∝ f^2) with hysteresis losses (∝ f).
- Assuming saturation automatically increases hysteresis without time variation.
Final Answer:
Hysteresis is most apparent when the current through the coil of an electromagnet changes frequently
Discussion & Comments