A transformer has primary turns Np and secondary turns Ns. If the input voltage is 480 V and the turns ratio Ns/Np = 0.5, what is the output voltage?

• A. 480 V
• B. 960 V
• C. 240 V
• D. 120 V

Answer: (C)

Voltage in the secondary is scaled from the primary by the turns ratio: Vs = Vp × (Ns/Np). Here, the input (primary) voltage is 480 V and the turns ratio Ns/Np is 0.5, so the output voltage is 480 × 0.5 = 240 V. Since the secondary has fewer turns than the primary, this is a step-down transformation. The other voltages would require different turns ratios (1:1 for 480 V, 2:1 to get 960 V, 1:4 to get 120 V, etc.), so 240 V is the correct result.