What is the voltage output of a transformer with a 500-turn primary and a 1500-turn secondary when 120 VAC is applied to the primary?

The voltage ratio of a transformer is directly proportional to its turns ratio. To find the turns ratio, divide the number of secondary turns by the primary turns. In this case, 1500 secondary turns divided by 500 primary turns equals a ratio of 3. Since it is a step-up transformer with a ratio of 3, you multiply the primary voltage by 3. Applying 120 VAC to the primary yields an output of 120 x 3 = 360 volts on the secondary. A common mistake is reversing the math and dividing 120 by 3, which results in the distractor of 40 volts. Always check if the secondary has more turns; if so, the voltage must step up.