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Hysteresis
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Magnetisation lags the field, tracing a loop.
Magnetisation lags behind the field, forming a loop in B–H; the area is energy lost per cycle. Hard magnets have wide loops; transformer cores have narrow loops.
Permanent magnets need a wide loop; electromagnets a narrow one.
Remanence and coercivity describe the loop.
In more detail
Hysteresis describes how the magnetisation of a ferromagnet lags behind the applied field. The loop shows the remanence and coercivity, which determine whether a material is magnetically hard or soft.
Real-world uses
- Soft magnets for transformers have narrow loops to reduce energy loss.
- Hard magnets for speakers and motors have wide loops to retain magnetism.
- Engineers designing transformers and motors choose cores with narrow hysteresis loops to reduce energy losses.
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Frequently asked questions
What is coercivity?
The reversed field needed to bring the magnetisation back to zero.
Why does a loop matter?
The area of the loop is the energy lost per cycle in the material.
What does hysteresis cost in energy?
Each cycle of magnetisation dissipates energy as heat, which is why low-loss materials are preferred in transformers.
Related topics in Magnetism & Induction
Magnetic dipole moment · Magnetic materials · Ferromagnetism and domains · Curie temperature · Electromagnets · Permanent magnets