For a transformer with its secondary winding left open-circuited (no load connected), which statement best describes the secondary side condition under normal operation?

Introduction / Context:
Transformers operate by magnetic coupling between primary and secondary windings. The behavior changes dramatically between loaded and unloaded (open-circuit) conditions. Knowing what happens on the secondary when it is not connected to a load is crucial for measurement, safety, and fault diagnosis.

Given Data / Assumptions:

• Secondary winding is open-circuited (no load).
• Primary is energized at its rated voltage and frequency.
• Transformer is healthy and designed for the operating frequency.

Concept / Approach:
With the secondary open, the transformer still establishes a mutual magnetic flux and thus an induced secondary voltage proportional to the turns ratio. However, since the circuit is open, no continuous path exists for current on the secondary; hence, the steady-state secondary current is essentially zero (ignoring tiny capacitive leakage). The primary still draws a small magnetizing current to establish core flux and to cover core loss.

Step-by-Step Solution:
Apply Faraday’s law: an induced EMF appears on the secondary proportional to N_secondary.Check circuit completion: with open terminals, current cannot flow.Conclude: secondary current is zero in steady state; secondary voltage is present but no load current flows.

Verification / Alternative check:
Measuring with a voltmeter across an unloaded secondary shows the rated RMS voltage. Using an ammeter in series with a still-open terminal indicates no current flow. Primary input current is small (magnetizing and core-loss components).

Why Other Options Are Wrong:
“Secondary voltage increases” is generally false; it stays near nominal (slight rise possible in regulation, but not an increase trend as stated).

“No secondary voltage” contradicts transformer action.

“Secondary current increases” is the opposite of open-circuit behavior.

“Secondary power equals primary power” is incorrect; with no load, real power transfer to the secondary is near zero aside from losses.

Common Pitfalls:
Confusing voltage presence with current flow; voltage can be present with zero current if the circuit is open.

Final Answer:
no secondary current flows