If current flow is in the same direction in the primary and secondary terminals, the polarity is subtractive.

• A. Unknown
• B. Additive
• C. Subtractive
• D. Neutral

Answer: (C)

Polarity in a transformer is about whether the voltages from the two windings aid or oppose each other when the windings are connected in series. The dot convention shows how to judge this: when currents flow in the same physical direction through the windings (entering or leaving the same ends relative to the dots), the induced voltages appear with opposite instantaneous polarity at the corresponding ends. That opposition is what we call subtractive polarity. So, if the primary and secondary currents run in the same direction, the secondary voltage tends to oppose the primary voltage in the series connection, leading to subtractive polarity. In contrast, currents in opposite directions would cause the voltages to add (additive).