In transformer documentation and circuit diagrams, which convention is used to indicate the instantaneous polarity (phase relationship) between primary and secondary windings?

Introduction / Context:
When two transformer windings are magnetically coupled, it is important to know which ends of the coils rise and fall in voltage together. This phase relationship affects series-aiding versus series-opposing connections, rectifier phasing, and feedback polarity in amplifiers.

Given Data / Assumptions:

• We are concerned with indicating polarity/phase, not just magnitude.
• Standard schematic symbols and drafting practices are assumed.
• The relationship applies at any instant for sinusoidal or non-sinusoidal excitation.

Concept / Approach:
Dot notation places a small dot at one end of each coupled winding. If the voltage at the dotted end of the primary becomes positive relative to its undotted end, the dotted end of the secondary simultaneously becomes positive relative to its undotted end (ignoring leakage and phase shifts). This convention communicates instantaneous polarity and therefore phase without ambiguity.

Step-by-Step Solution:
Identify the need: we must show which ends of primary/secondary are in-phase.Recall the standard: schematic dots mark corresponding ends of windings.Apply meaning: a rise at a dotted primary end corresponds to a rise at the dotted secondary end.Select the correct option: dot notation.

Verification / Alternative check:
Textbooks and manufacturer datasheets consistently use polarity dots to define instantaneous voltage relationships. Turns ratio labels do not convey phase by themselves.

Why Other Options Are Wrong:
Color-coded wires and casing colors vary by vendor and are not a universal schematic standard.

Winding ratios indicate magnitude relationships, not phase.

Arrowheads on cores are not a standard polarity convention for transformers.

Common Pitfalls:
Assuming the higher-turns winding is always drawn on top or that lead colors define polarity. Only the dot convention is universally meaningful on schematics.

Final Answer:
dot notation (polarity dots)