What is a transformer?

What is a transformer?

• A. A device that stores energy in a magnetic field.
• B. A device that increases or decreases the voltage of alternating current.
• C. A device that switches DC to AC.
• D. A device that filters noise.

Answer: (B)

A transformer changes the voltage of alternating current by transferring energy between two or more coils through a magnetic core. The essential idea is electromagnetic induction: when AC flows in the primary winding, it creates a changing magnetic field that induces a voltage in the secondary winding, and the turns ratio determines whether the voltage is stepped up or down. This relies on a time-varying current; a steady DC input would produce a constant magnetic field and would not sustain energy transfer, so a transformer won’t work with DC alone. Descriptions of storing energy in a magnetic field point to an inductor, which stores energy but doesn’t continuously transfer it to a second circuit. Descriptions of switching DC to AC refer to an inverter, not a transformer. Descriptions of filtering noise refer to a filter, which is a different function. In practice, a transformer lets you adapt the mains voltage to a level suitable for a device while keeping the same frequency.

A transformer changes the voltage of alternating current by transferring energy between two or more coils through a magnetic core. The essential idea is electromagnetic induction: when AC flows in the primary winding, it creates a changing magnetic field that induces a voltage in the secondary winding, and the turns ratio determines whether the voltage is stepped up or down. This relies on a time-varying current; a steady DC input would produce a constant magnetic field and would not sustain energy transfer, so a transformer won’t work with DC alone. Descriptions of storing energy in a magnetic field point to an inductor, which stores energy but doesn’t continuously transfer it to a second circuit. Descriptions of switching DC to AC refer to an inverter, not a transformer. Descriptions of filtering noise refer to a filter, which is a different function. In practice, a transformer lets you adapt the mains voltage to a level suitable for a device while keeping the same frequency.