Transformer nonideal effect — name the phenomenon: Identify the effect that occurs when some of the primary’s magnetic flux does not link the core path to the secondary and instead travels through surrounding air paths.

Introduction / Context:
Real transformers deviate from the ideal due to losses and imperfect coupling. Understanding each nonideal effect is essential for predicting voltage regulation, efficiency, and bandwidth.

Given Data / Assumptions:

• Primary and secondary windings share a core but not all flux is perfectly confined.
• Some field lines escape the core and loop through air or structural parts.
• We classify this behavior among nonideal effects.

Concept / Approach:
Magnetic flux leakage refers to the portion of magnetic flux generated by the primary that fails to couple to the secondary. Leakage effectively inserts series inductances and reduces the coupling coefficient k, lowering mutual inductance and altering transient response.

Step-by-Step Solution:

Verification / Alternative check:
Designers reduce leakage by interleaving windings, using high-permeability cores, and minimizing air gaps. Measurement of leakage inductance in equivalent circuits confirms the effect quantitatively.

Why Other Options Are Wrong:
Hysteresis loss: Energy lost per cycle in the core due to magnetization reversal; not uncoupled flux per se.

Winding resistance: Copper loss (I^2*R), unrelated to flux paths.

Winding capacitance: Parasitic capacitive effects between turns/layers; not flux leakage.

Common Pitfalls:
Confusing leakage flux with fringing flux at air gaps; both involve air paths but have different implications. Equating leakage with core loss; they are distinct.

Final Answer:
Magnetic flux leakage