Electromagnetic Induction Principle

Steps:

• Transformers rely on mutual induction: alternating current in the primary coil creates a changing magnetic field.
• This field links with the secondary coil, inducing electromotive force (e.m.f.) via Faraday's law.
• Evaluate options: A matches induction; B misstates core purpose; C and D confuse current types.
• Confirm A as the only accurate statement.

Why A is correct:

• Faraday's law states that a changing magnetic flux through a coil induces e.m.f., which occurs in the secondary coil due to the primary's alternating field.

Why the others are wrong:

• B: Iron core provides high magnetic permeability to concentrate flux, not electrical conductivity (it's laminated to minimize currents).
• C: Transformers step up/down AC voltage but do not convert to direct current.
• D: Transformers require AC input for changing fields; DC-to-AC conversion needs an inverter.

Final answer: A