In an ideal transformer with Np:Ns = 3:1, the secondary voltage is what fraction of the primary voltage?

• A. One third of
• B. Three times
• C. The same as
• D. Two thirds of

Answer: (A)

Voltage in an ideal transformer scales with the turns ratio, so the secondary voltage equals the primary voltage times Ns/Np. With Np:Ns = 3:1, Ns/Np = 1/3, so the secondary voltage is one third of the primary voltage. In other words, the device steps the voltage down by a factor of three (and, in an ideal case, currents shift inversely to conserve power). The other options would require different turns ratios: three times would mean the secondary has three times as many turns as the primary, the same voltage would require equal turns, and two thirds would require the secondary to have two thirds as many turns as the primary.