Is it possible for a transformer to be built without an iron core?

• A. Yes
• B. No
• C. Sometimes
• D. Always

Answer: (B)

The essential idea is how a transformer uses a magnetic path to transfer energy between windings. The core provides a low-reluctance route for the magnetic flux, concentrating it so that the changing flux in one winding strongly links the other. Without any core, the magnetic field would fan out into surrounding space, causing very weak coupling and requiring impractically large windings or resulting in little energy transfer. For most practical transformers, a magnetic material like iron (or ferrite at high frequencies) is used to make the coupling efficient. There are niche cases—air-core transformers—where no iron or ferrite core is used, but they’re uncommon for typical power or audio transformers because they’re much less efficient and bulkier. So, in standard practice, a transformer is not built without some magnetic core.