Electronic, magnetic and optical materials
Which correctly describes a soft magnetic material suitable for a transformer core?
- ALarge coercivity and a broad hysteresis loop with a large enclosed area
- BSmall coercivity and a narrow hysteresis loop with a small area
- CA large remanence is most important, and coercivity does not matter
Show answer and explanation
Answer: B. Small coercivity and a narrow hysteresis loop with a small area
In an AC core the magnetization reverses every cycle, so energy proportional to the area of the hysteresis loop is lost each cycle. A soft magnetic material with small coercivity and a narrow loop is therefore needed. High permeability and saturation flux density are also required, as is high electrical resistivity to reduce eddy-current losses; grain-oriented electrical steel (silicon steel), ferrites and amorphous alloys are used. Large coercivity and a large loop area are characteristics of hard magnetic materials (permanent magnets) such as Nd-Fe-B and ferrite magnets. For permanent magnets, both a large remanence and a large coercivity are important.
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