A transformer has 1000 turns on the primary side and 2000 on the secondary. What is the output if the input is 120v?

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

Answer: (A)

Voltage in a transformer scales with the turns ratio. In an ideal transformer, Vs = Vp × (Ns/Np). Here Ns is 2000 and Np is 1000, so the ratio is 2. With an input of 120 V on the primary, the output becomes 120 × 2 = 240 V. This is a step-up transformation. In real transformers, there are small losses, but the voltage will be about 240 V.