The primary winding of a transformer has 250 turns, and the secondary has 500 turns. If the input voltage is 120 volts, what is the secondary voltage?

The voltage across a transformer's windings is directly proportional to the number of turns of wire in each winding. This relationship is expressed by the turns ratio formula: Voltage(secondary) / Voltage(primary) = Turns(secondary) / Turns(primary). In this scenario, the secondary winding has exactly twice as many turns as the primary winding (500 turns versus 250 turns). Because the number of turns doubles, this acts as a step-up transformer that will double the voltage. Multiplying the 120-volt input by 2 yields a secondary voltage of 240 volts. If you mistakenly assumed it was a step-down transformer, you might divide by 2 and incorrectly select 60 volts.