Magnetomotive Force (MMF)

F = N × I

Quick answer

This calculator solves F = N × I (ampere-turns) for MMF. With Number of Turns 0.5, Current 2 A, the result is 1 A·t. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

MMF (A·t)
—

Formula

F = N × I (ampere-turns)

Description

Magnetomotive force is the magnetic-circuit analogue of voltage: it is the "drive" that pushes magnetic flux around a core, produced by a coil of N turns carrying current I. Doubling either the turns or the current doubles the MMF and therefore the flux for a given reluctance. It is the source term in the magnetic Ohm’s law.

Variables

  • F — Magnetomotive force (ampere-turns)
  • N — Number of coil turns
  • I — Coil current (A)

Practical Notes

MMF drives flux through reluctance just as EMF drives current through resistance: Φ = F / S. Increasing turns raises MMF without raising current, which is why electromagnets use many turns.

Symbols and units

Symbol Meaning Default unit Accepted units
F MMF A·t A·t, kA·t
N Number of Turns — —
I Current A pA, nA, µA, mA, A, kA

Step by step

  1. 1. What you know: Number of Turns 0.5, Current 2 A
  2. 2. The relation: F = N × I (ampere-turns)
  3. 3. Substitute: N = 0.5, I = 2 A
  4. 4. Result: MMF = 1 A·t

Worked examples

Minimum range

Given: Number of Turns 0.025, Current 2 mA

Result: MMF = 5 × 10⁻⁵ A·t

Low range

Given: Number of Turns 0.25, Current 20 mA

Result: MMF = 0.005 A·t

Typical

Given: Number of Turns 0.5, Current 2 A

Result: MMF = 1 A·t

High range

Given: Number of Turns 0.8, Current 100 A

Result: MMF = 80 A·t

Maximum range

Given: Number of Turns 8, Current 1 kA

Result: MMF = 8 kA·t

Solving for each variable

Solve for MMF

Number of Turns 0.025, Current 2 mA → 5 × 10⁻⁵ A·t

Solve for Number of Turns

MMF 10 A·t, Current 2 mA → 5000

Solve for Current

MMF 10 A·t, Number of Turns 0.025 → 0.4 kA

How MMF changes with Number of Turns

Number of Turns (input) MMF (result)
0.05 0.1 A·t
0.125 0.25 A·t
0.25 0.5 A·t
0.375 0.75 A·t
0.5 1 A·t
0.75 1.5 A·t
1 2 A·t
2 4 A·t
3.5 7 A·t
5 10 A·t

The same result in other units

Unit Value
A·t 1
kA·t 0.001

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Frequently asked questions

How do you calculate Magnetomotive Force (MMF)?

Use F = N × I (ampere-turns). With Number of Turns 0.5, Current 2 A, MMF works out to 1 A·t.

What is the formula for Magnetomotive Force (MMF)?

The formula is F = N × I (ampere-turns). Magnetomotive force is the magnetic-circuit analogue of voltage: it is the "drive" that pushes magnetic flux around a core, produced by a coil of N turns carrying current I.

How do you find Number of Turns when you know the other values?

Rearrange for Number of Turns: with MMF 10 A·t, Current 2 mA, Number of Turns is 5000.

How do you find Current when you know the other values?

Rearrange for Current: with MMF 10 A·t, Number of Turns 0.025, Current is 0.4 kA.

What units does Magnetomotive Force (MMF) use?

MMF is shown in A·t, kA·t. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Magnetics & Transformers formulas →
Transformer EMF Equation Transformer VA Rating Transformer Voltage Regulation Transformer Current Ratio Transformer Copper Loss Transformer Iron (Core) Loss Transformer Turns-per-Volt Transformer Impedance Matching

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