In a transformer with turns ratio 10:1 (step-down), which statement correctly describes current flow?

In a transformer with turns ratio 10:1 (step-down), which statement correctly describes current flow?

• A. The current in the primary and secondary will be the same.
• B. The current in the secondary will be approximately 10 times higher than the current in the primary
• C. The current in the primary will be approximately 10 times higher than the current in the secondary.
• D. Transformers cannot have 10:1 step down ratios.

Answer: (D)

In an ideal transformer, voltage is proportional to the turns, and current varies inversely so power stays the same (Vp/Vs = Np/Ns and Ip/Is = Ns/Np). With a 10:1 step-down, Vs ≈ Vp/10, and to keep power roughly equal, Vp Ip ≈ Vs Is leads to Is ≈ 10 Ip. So the secondary current is about ten times the primary current. This is why the correct idea is that the current in the secondary will be approximately 10 times higher than the current in the primary. A 10:1 turn ratio is perfectly feasible, so the statement claiming such a ratio cannot exist is not correct.

In an ideal transformer, voltage is proportional to the turns, and current varies inversely so power stays the same (Vp/Vs = Np/Ns and Ip/Is = Ns/Np). With a 10:1 step-down, Vs ≈ Vp/10, and to keep power roughly equal, Vp Ip ≈ Vs Is leads to Is ≈ 10 Ip. So the secondary current is about ten times the primary current. This is why the correct idea is that the current in the secondary will be approximately 10 times higher than the current in the primary. A 10:1 turn ratio is perfectly feasible, so the statement claiming such a ratio cannot exist is not correct.