Magnetomotive force (MMF) calculation: A coil of 8 turns carries a steady current of 3 A. Determine the MMF in ampere–turns (At).

Introduction / Context:Magnetomotive force (MMF) is a fundamental quantity in electromagnetics and electrical machines. It represents the 'driving force' that establishes magnetic flux in a magnetic circuit, analogous to how a voltage source drives electric current in an electric circuit.

Given Data / Assumptions:

• Number of turns, N = 8.
• Current through the coil, I = 3 A (direct current, steady state).
• Air gaps, core properties, and leakage are irrelevant for MMF calculation; only N and I matter.

Concept / Approach:

The definition of MMF for a simple coil is MMF = N * I, expressed in ampere–turns (At). This linear relation comes from summing the magnetizing effect of each turn carrying current I around the magnetic path.

Step-by-Step Solution:

Verification / Alternative check:

If the current were doubled or the turns doubled, MMF would double accordingly, confirming proportionality to both N and I. The units ampere–turns reflect 'A per turn' summed across turns, consistent with the definition.

Why Other Options Are Wrong:

240 At and 2,400 At incorrectly multiply by extra powers of 10. 2.4 At divides instead of multiplies. 0.375 At would correspond to I/N rather than N*I, which is incorrect.

Common Pitfalls:

Confusing MMF with magnetic flux or flux density, or forgetting that MMF depends only on turns and current, not on core dimensions or permeability.

Final Answer:

24 At