What voltage results on the secondary of a transformer with a 400 turns primary and 200 turns in the secondary when 240 volts are applied to the primary?

• A. 240 volts
• B. 480 volts
• C. 60 volts
• D. 120 volts

Answer: (D)

Voltage on the secondary follows the turns ratio. In an ideal transformer, Vs = Vp × (Ns/Np), so the voltage scales with the number of turns on each winding. Here, the primary has 400 turns and the secondary has 200, giving Ns/Np = 200/400 = 0.5. With 240 V applied to the primary, the secondary voltage is 240 × 0.5 = 120 V. This is a step-down by a factor of two because there are half as many turns on the secondary.

In real transformers there are small losses, but the result is still about 120 V. The other options would require different turn ratios: equal turns would yield 240 V, more secondary turns would yield 480 V, and a much smaller secondary voltage (like 60 V) would require a 0.25 ratio.