Eddy currents can be reduced by

Analyze the question Eddy currents are unwanted circulating currents induced in a metal core (such as the iron core of a transformer or dynamo) when the magnetic flux through it changes. They waste energy as heat. The question asks how to reduce them.

Concept Eddy currents flow in closed loops inside the bulk of the metal. To reduce them, we must break up or restrict these loops, so the resistance of the path they travel in is increased. The usual methods are:

• Laminating the core, which means using thin sheets of metal insulated from one another instead of a solid block.
• Cutting slots or making holes in the metal plates, which interrupts the loop paths.

Step-by-step evaluation of the options

• A. Coil of high resistance: This affects the current in the coil (the winding). It does not affect the eddy currents in the core, so it is incorrect.
• B. Winding the coil on a soft iron core: Soft iron is a conductor, so a solid core actually supports large eddy currents. It is used to strengthen the magnetic field, not to reduce eddy currents. Incorrect.
• C. Creating holes in the metal plates: The holes break up the paths available to the eddy currents, which raises the resistance to them and reduces their size. Correct.
• D. Coil of low resistance: Like A, this concerns the coil and not the core, so it is incorrect.

Answer: The correct option is C.

Exam tip Remember "Eddy = Edit the core". Think of lamination, slits, or holes in the core, never the coil's resistance. Whenever you see eddy currents in an exam, ask yourself, "What breaks up the current loops in the core?"