If a transformer has primary 80 turns and secondary 40 turns, the turns ratio is.

• A. 1:2
• B. 2:1
• C. 1:1
• D. 3:1

Answer: (B)

Turns ratio tells you how many times more (or fewer) turns the primary has compared with the secondary, and it sets how the voltage and current are scaled in an ideal transformer. With 80 turns on the primary and 40 on the secondary, the ratio is 80:40, which simplifies to 2:1. So the turns ratio is 2:1, meaning the primary has twice as many turns as the secondary and the transformer steps the voltage down by a factor of two (Vp/Vs = 2, so Vs = Vp/2). Correspondingly, the current goes the other way: Is = 2Ip, so the secondary current is twice the primary current to keep power roughly the same (VpIp ≈ Vs*Is). Ratios like 1:2, 1:1, or 3:1 don’t match the given turn counts.