Transformers — qualitative comparison: In a step-down transformer operating under normal conditions, which voltage is larger?

Introduction / Context:
Transformers change AC voltage levels based on the turns ratio between primary and secondary windings. Recognizing which side is higher for a step-down device is essential in power supplies and isolation stages.

Given Data / Assumptions:

• A step-down transformer is specified (turns ratio Np:Ns > 1).
• We compare RMS voltages under nominal operation.
• Losses and regulation are ignored for this qualitative question.

Concept / Approach:
The ideal transformer relation is Vp/Vs = Np/Ns. For step-down, Np > Ns, so Vp > Vs. Therefore, the primary voltage is larger than the secondary voltage by the turns ratio factor.

Step-by-Step Solution:
Identify: “step-down” implies Np/Ns > 1.Apply relation: Vp/Vs = Np/Ns → Vp > Vs.Select “Primary voltage.”

Verification / Alternative check:
Example: Np:Ns = 10:1. If Vp = 230 V RMS, then Vs ≈ 23 V RMS (ideal), confirming primary > secondary.

Why Other Options Are Wrong:
(b) Secondary is lower in a step-down. (c) Equality would be an isolation (1:1) transformer. (d) Frequency does not reverse step-down vs step-up; it matters for core design, not the basic ratio.

Common Pitfalls:
Confusing “step-down” with “step-up” or mixing current and voltage relations (current increases on the step-down side).

Final Answer:
Primary voltage.