A transformer is required to give 120V from a 240V mains supply. If the primary has 5500 turns, how many turns has the secondary?

Analyze the question: A step-down transformer changes 240 V to 120 V. The primary has 5500 turns, and we need the number of turns on the secondary.

Concept: For an ideal transformer, the voltage ratio equals the turns ratio:

Vs / Vp = Ns / Np

Solution:

• Vp = 240 V
• Vs = 120 V
• Np = 5500

Ns = Np × (Vs / Vp)

Ns = 5500 × (120 / 240)

Ns = 5500 × 0.5

Ns = 2750 turns

Check: The voltage is halved (240 V → 120 V), so the secondary should have half the turns of the primary. Half of 5500 is 2750. ✔

Answer: D. 2750

Tip: Look at the voltage ratio first. If the voltage is halved, the turns are halved. A step-down transformer always has fewer secondary turns than primary turns, so you can eliminate E (11000) immediately, since it is larger than 5500.