In an ideal transformer with 50 turns on the primary and 100 turns on the secondary, what is the voltage relationship?

• A. Secondary voltage equals primary voltage.
• B. Secondary voltage is double the primary voltage.
• C. Secondary voltage is half the primary voltage.
• D. Voltage cannot be determined.

Answer: (B)

In an ideal transformer, voltages scale with the turns ratio. The secondary-to-primary voltage equals the secondary-to-primary turns ratio: V_s / V_p = N_s / N_p. Here N_s = 100 and N_p = 50, so the ratio is 100/50 = 2. Therefore the secondary voltage is twice the primary voltage: V_s = 2 V_p. For example, if the primary has 230 V, the secondary would be about 460 V (ignoring losses). The current reverses proportionally so that power stays the same: I_s = (N_p / N_s) I_p = 0.5 I_p. Real transformers have small losses, but the basic relationship holds.