Transformers: Practice Problem & Solution
The core of a transformer is laminated because: (2006)
Short Solution (Best for NEET):
To solve this problem, we apply the core principles of Transformers. Understanding the underlying formula is key to arriving at the correct answer below:
A solid metal core allows large eddy currents, which lead to significant energy loss as heat.
By laminating the core, its electrical resistance is increased.
This restricts the paths of the eddy currents and minimizes the associated energy losses.
Detailed Solution (Best of Understanding Complex Concepts)
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Origin of Eddy Currents: A transformer operates on alternating current (AC), which produces a continuously varying magnetic flux in the core. According to Faraday's Law of Electromagnetic Induction, this changing magnetic flux induces an electromotive force (EMF) not only in the secondary coil but also within the bulk of the conducting iron core itself.
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Energy Loss (Joule Heating): These induced EMFs cause localized, circulating currents within the core, known as Eddy currents. Because the core material has electrical resistance ($R$), these currents dissipate electrical energy in the form of heat (given by $I^2R$). This heat represents wasted energy, significantly reducing the efficiency of the transformer.
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Effect of Lamination: To combat this, the core is not made of a single solid metallic block. Instead, it is constructed from multiple thin sheets of steel or iron, known as laminations. Each sheet is coated with a thin layer of insulating material (like varnish or oxide) to electrically isolate it from the adjacent sheets.
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How Lamination Minimizes Loss: The insulating layers run parallel to the magnetic field but perpendicular to the direction the eddy currents want to flow. By breaking a large solid core into thin, insulated slices, the effective cross-sectional area for the current loop is restricted. This drastically increases the electrical resistance against the eddy currents, reducing their magnitude. Consequently, the $I^2R$ heat dissipation is minimized.
Therefore, laminating the core is a specific design choice made to minimize energy losses due to eddy currents.
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