Magnetic circuit analogy: which property of a magnetic circuit is directly analogous to voltage in an electrical circuit?

Introduction / Context:
Magnetic circuits are often taught using an analogy to electrical circuits to make design intuition easier. In this analogy, one must map each magnetic quantity to its electrical counterpart to reason about cores, air gaps, and excitation requirements. Knowing which parameter corresponds to “voltage” is key to understanding how coils drive flux.

Given Data / Assumptions:

• Magnetic circuits are treated using lumped-parameter models.
• The analogy compares voltage, current, and resistance to their magnetic counterparts.
• We seek the magnetic quantity that “pushes” flux through a magnetic path.

Concept / Approach:
In the analogy: magnetomotive force (MMF, usually NI where N = turns and I = current) corresponds to voltage; magnetic flux Φ corresponds to current; reluctance ℜ corresponds to resistance. Flux density B relates to flux per unit area and is not directly the “driving force.” MMF is the cause, flux is the effect, and reluctance is the opposition—precisely mirroring Ohm’s law as Φ = MMF / ℜ in magnetic form.

Step-by-Step Solution:
Recall definitions: MMF drives magnetic flux through a magnetic path.Apply the analogy: Voltage ↔ MMF, Current ↔ Flux, Resistance ↔ Reluctance.Identify the required counterpart of voltage: MMF.Select “Magnetomotive force.”

Verification / Alternative check:
Using Φ = MMF / ℜ, increasing NI (more turns or current) raises flux for a given reluctance, just as raising voltage increases current for a given resistance per Ohm’s law I = V / R.

Why Other Options Are Wrong:
Flux density is analogous to current density, not voltage. “Number of lines of force” loosely relates to total flux, not the driving force. Reluctance is the magnetic analog of resistance, not voltage. “None” is wrong because MMF is the correct counterpart.

Common Pitfalls:
Confusing B (flux density) with H (magnetizing field); forgetting that the analogy is useful but has limits when materials saturate or at high frequencies where losses become dominant.

Final Answer:
Magnetomotive force