Transformer operation — Which statement correctly describes what a transformer will have or maintain in normal operation?

Introduction:
A transformer is a static electromagnetic device that transfers energy between circuits via mutual induction. Understanding which characteristics are intrinsic vs. situational prevents confusion in specifications and testing.

Given Data / Assumptions:

• Conventional power or signal transformer with two windings.
• Same frequency present on both windings under ideal conditions.
• No commutation or moving parts.

Concept / Approach:

Every transformer, by definition, has at least two windings (primary and secondary). Currents and power depend on load conditions; frequency is the same on both sides (neglecting tiny phase shifts), since the magnetic coupling does not change the input frequency.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets always specify turns for both windings; frequency on secondary equals primary’s frequency in steady state.

Why Other Options Are Wrong:

• primary and secondary current: Secondary current can be near zero at no load.
• primary wattage producing secondary current: Wording is misleading; power transfer depends on load and losses.
• different frequencies: Incorrect; frequency is preserved.
• commutator: Transformers have no rotating parts.

Common Pitfalls:

• Assuming secondary current exists without load; only magnetizing current flows then.
• Thinking a transformer can change frequency; it cannot.

Final Answer:

primary and secondary windings