A coil of wire wound along a core of uniform diameter is called what?

• A. Transformer
• B. Solenoid
• C. Inductor
• D. Rotor

Answer: (B)

A long, cylindrical coil of wire around a core is called a solenoid. The word describes the geometry: many turns of wire arranged along a straight, tubular form, producing a magnetic field that runs along the axis of the coil. The uniform-diameter core helps guide that magnetic flux, giving a predictable, strong field and a well-defined inductance.

This setup isn’t a transformer because there’s only a single winding, and a transformer relies on mutual coupling between two or more windings on a shared core. It’s also not a rotor, which is a rotating part in machines. While a coil like this can act as an inductor (storing energy in its magnetic field), the term solenoid emphasizes the coil’s shape and arrangement, making it the most precise label for this configuration.