How can energy loss be minimized through Eddy-current?

Analysis

The question asks for the method used to minimize energy loss caused by Eddy currents in electrical machines like transformers and motors.

Concept Explanation

Eddy currents are circular loops of induced current that flow within the core of a transformer or motor when it is subjected to a changing magnetic field. According to Lenz's Law, these currents create their own magnetic fields that oppose the change, leading to:

1. Energy loss: Energy is dissipated as heat ($I^2R$ loss).
2. Overheating: This can damage the insulation of the device.

To minimize these losses, engineers use a technique called lamination. Instead of using a solid block of metal for the core, they use thin sheets (laminations) of soft iron. Each sheet is coated with an insulating material (like varnish). This insulation breaks the path of the eddy currents, forcing them to stay within a very small area, which significantly reduces their magnitude and the resulting heat loss.

Step-by-Step Solution

1. Identify the cause: Eddy currents flow in solid metal cores because the metal provides a low-resistance path for the induced currents to circulate.
2. Evaluate the options: • A (High resistance wire): This relates to reducing current in a circuit, not the eddy currents within a core. • B (Insulated soft iron wires/sheets): By using thin, insulated sheets (laminations), the path for eddy currents is restricted, effectively minimizing energy loss. This is the standard engineering practice. • C (Low resistance wires): Low resistance would actually increase the flow of eddy currents, leading to more energy loss. • D (Turns of wires): This relates to the number of turns in a coil (transformer ratio), not the core material properties.
3. Conclusion: The use of insulated soft iron laminations is the correct physical principle to minimize eddy current losses.

Correct Answer

The correct option is B.

Exam Tip

Whenever you see a question about "Eddy currents" in JAMB or WASSCE, look for keywords like "Lamination" or "Insulated sheets." Remember: Lamination = Less Eddy Current = Less Heat Loss.