A laminated iron core has reduced eddy current losses because

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Option B: Laminations are insulated from each other

Explanation & Concepts:
A laminated iron core consists of thin sheets of silicon steel coated with a thin layer of insulating material. By breaking the electrical continuity within the core, these insulation layers significantly increase the resistance path for eddy currents, thereby reducing the power loss occurring due to $P_e = K_e f^2 B_m^2 t^2$.

Working Principle: According to Faraday's law, a time-varying magnetic flux induces EMF in the core, creating eddy currents. Because the magnitude of these currents is proportional to the area of the loop perpendicular to the flux, laminating the core into thin segments forces these currents to stay within smaller areas, effectively increasing the core resistance and reducing the $I^2R$ power loss.

Key Formulas: $P_e = K_e f^2 B_m^2 t^2$ — Eddy current loss equation where $t$ is the thickness of lamination; $R_{effective} = \rho \frac{l}{A}$ — Illustrating how lamination geometry alters path resistance

Key Points: Eddy currents are circulating currents induced in the core by changing magnetic fields.; Lamination does not reduce hysteresis loss, which depends on core material properties.; Silicon steel is often used to further reduce hysteresis loss by increasing resistivity.; The insulation between laminations is typically a thin layer of varnish or oxide.

Advantages: Significant reduction in core heating; Improved transformer and machine efficiency

Disadvantages: Increased core manufacturing cost; Slight reduction in effective magnetic cross-sectional area (stacking factor)

Applications: Power transformers; Induction motors; High-frequency inductors

Additional Info: The stacking factor typically ranges from 0.9 to 0.95, representing the ratio of actual iron volume to total volume.. Option A is irrelevant to magnetic core eddy losses. Option C is a property of air-gap design. Option D is simply the orientation and does not address the current path constraint.

Answer: B is correct — Laminations are insulated from each other to increase the electrical resistance in the path of eddy currents, thereby minimizing induced current magnitude.

Exam Tip: Always remember: Eddy current loss is proportional to the square of the lamination thickness ($t^2$). Therefore, using thinner laminations is the most effective way to minimize these losses at high frequencies.

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Option A: More conductor can be used with less DC resistance in coil

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Option C: Magnetic flux is concentrated in the air gap of the core

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Option D: Laminations are stacked vertically

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