This larger primary and secondary coil set is designed so that teachers can provide a larger, more visible demonstration in a classroom setting. The secondary coil slides over the primary coil, and the soft iron core slides into either or both. This rugged device is sensitive enough to be used with voltmeters instead of galvanometers. The coils are wound around hollow plastic cores, with a turns ratio of approximately 2 (@380) to 1 (@200). Provides a look at electromagnetic induction, ferromagnetism and transformer theory.