Magnetomotive force (mmf) unit: Ampere–turn (AT) is the standard unit of mmf in magnetic circuits. True or false?

Introduction / Context:
Magnetomotive force drives magnetic flux through a magnetic circuit in much the same way that electromotive force drives current through an electric circuit. Knowing its unit and meaning is foundational for inductor and transformer design.

Given Data / Assumptions:

• Number of turns: N.
• Current through the coil: I (amperes).
• Magnetomotive force: mmf = N * I.

Concept / Approach:

By definition, mmf equals the product of current and turns. The natural unit is ampere–turn (AT). In SI base terms, mmf can also be expressed in amperes, but ampere–turn emphasizes the winding's role and is widely used in magnetic circuit calculations and datasheets.

Step-by-Step Solution:

Verification / Alternative check:

Check datasheets of electromagnetic actuators and transformers; winding specifications list ampere–turns required to achieve a target flux density or force, reinforcing AT as the practical unit of mmf.

Why Other Options Are Wrong:

• “False” would disregard the universally accepted mmf expression and its unit. While mmf can be dimensionally treated as amperes, AT is the conventional and clearer unit in engineering practice.

Common Pitfalls:

Confusing mmf (a cause) with flux Φ (an effect) or flux density B. Also, mixing up AT (mmf) with A/m (field strength, H), which depends on path length.

Final Answer:

True