SI unit of magnetomotive force (mmf) in electromagnetic circuits Identify the correct SI unit for magnetomotive force, considering mmf = N * I for a coil with N turns carrying current I.

Introduction / Context:
Magnetomotive force (mmf) drives magnetic flux in a magnetic circuit analogous to how electromotive force drives current in an electric circuit. Understanding correct SI units prevents confusion when relating coil parameters, reluctance, and flux.

Given Data / Assumptions:

• Definition: mmf = N * I, where N is number of turns and I is current in amperes.
• Reluctance R_m relates mmf and flux via mmf = Φ * R_m.
• We use SI base units.

Concept / Approach:
Since N is a pure count (dimensionless), mmf carries the units of current. Thus, the SI unit for mmf is ampere (A). In practice, engineers often speak of ampere-turn (A·t) to emphasize that increasing turns multiplies the mmf, but this is not a distinct SI base unit.

Step-by-Step Solution:
Start from mmf = N * I.Dimensional analysis: N is dimensionless, I has unit A.Therefore, unit of mmf is A.

Verification / Alternative check:
Textbook tables list ampere (or ampere-turn as a descriptive derivative) for mmf; standards agree that the base SI unit reduces to ampere.

Why Other Options Are Wrong:
Weber (Wb) measures magnetic flux; tesla (T) measures flux density; volt (V) measures electrical potential difference. None represent mmf.

Common Pitfalls:

• Believing that ampere-turn is a separate SI unit; it is a convenient expression but dimensionally equivalent to ampere.
• Confusing mmf with magnetic field strength H, which has units A/m.

Final Answer:
A (ampere)