Transformer

Two coils sharing a magnetic core make a transformer, which changes an AC voltage up or down in proportion to the turns ratio while keeping the secondary electrically isolated from the primary. Because it works only with alternating current, circuits in this tag pair it with an AC source, usually with an oscilloscope on both windings, in step-up and step-down demonstrations, rectifier power supplies, battery chargers and transformer-coupled amplifiers. For example, "Step down transformer" lowers an AC supply to light a lamp at reduced voltage.