Final answer:
The primary and secondary coils of a transformer must be wound around the same ferromagnetic iron core to concentrate and enhance the magnetic field, ensuring effective induction according to Faraday's law.
Step-by-step explanation:
The student asks, Why are the primary and secondary coils of a transformer wrapped around the same closed loop of iron? To function properly, the primary and secondary coils of a transformer must be wound around a common ferromagnetic core, typically made of laminated iron. This core serves multiple purposes: it concentrates the magnetic field generated by the primary coil, enhances field strength, and ensures that the flux changes are efficiently transmitted to the secondary coil. According to Faraday's law of induction, a time-varying magnetic field will induce an electromotive force (EMF) in any circuit linked to that field. The iron core, by trapping and strengthening the magnetic field, makes sure that the change in current in the primary coil induces a current in the secondary coil, which is necessary for the transformer to work correctly. Thus, it is crucial for effective induction that both coils share the same magnetic circuit, which is provided by the laminated iron core.