Final answer:
The primary and secondary coils of a transformer are wrapped around the same iron core to efficiently transfer the magnetic field from one coil to the other, enhancing the transformer's efficiency in energy transfer.
Step-by-step explanation:
To guarantee that the magnetic field produced by the primary coil is efficiently transferred to the secondary coil, the transformer's primary and secondary coils are wound around the same closed loop of iron. This closed iron loop, also known as the core, serves as a conduit for the magnetic field, keeping it concentrated and improving the transformer's operating efficiency. Both coils can take full advantage of the magnetic field because they have a common core, which leads to the best possible induction and energy transfer.