Difference between Electromotive Force (EMF) and Magnetomotive Force (MMF)

Differences Digital Electronics Electronics & Electrical

The Magnetomotive force (MMF) in a magnetic circuit is analogous to the electromotive force (EMF) in an electric circuit. MMF is the factor responsible for driving the magnetic flux in a magnetic core, while the electromotive force EMF is the factor responsible for the flow of electric charge (or electrons) in an electric circuit.

What is Electromotive Force (EMF)?

The total amount of energy given to a unit charge by a source of energy such as generator, battery, etc. is known as electromotive force (or EMF) of the energy source. As the electromotive force has “force” in its name but technically, the EMF is not a force, rather it is energy given to per unit charge by a source of energy.

In an electric circuit, if W is the work done, Q is the total charge, then the EMF in the circuit is given by,

$$\mathrm{EMF\mathit{\, \mathrm{=}\, \frac{W }{Q}}}$$

Thus, EMF can also be defined as the work done in moving a unit charge once around an electric circuit.

The electromotive force or EMF is measured in volts, where 1 volt is equal to 1 joule per coulomb. The EMF is the factor in an electric circuit responsible for creating a potential difference between two points and hence for current flow.

What is Magnetomotive Force (MMF)?

The Magnetomotive force is the factor in a magnetic circuit which is responsible for establishing the magnetic flux in the circuit. The Magnetomotive force or MMF is defined as the work done in a magnetic circuit in moving a unit magnetic pole once around the magnetic circuit.

Basically, MMF is the magnetic pressure that tends to set up magnetic flux in a magnetic circuit. Mathematically, the Magnetomotive force is defined as the product of current and number of turns in a coil, i.e.

$$\mathrm{MMF\mathit{\, \mathrm{=}\, I\cdot N}}$$

Where, 'I' is the current flowing in a coil of 'N' turns. The MMF is measured in AT or Ampere Turns.

Difference between EMF and MMF

The following table highlights the key differences between the electromotive and the magnetomotive forces −

Parameter	Electromotive Force	Magnetomotive Force
Abbreviation	The abbreviated name used for electromotive force is EMF.	The abbreviated name used for Magnetomotive force is MMF.
Definition	The total amount of energy given to a unit electric charge by a source of energy to move once around the electric circuit is known as electromotive force or EMF.	The total amount of work done in moving a unit magnetic pole once around a magnetic circuit is known as Magnetomotive force or MMF.
Existence	The electromotive force exists in an electric circuit.	The Magnetomotive force exists in a magnetic circuit.
Measurement unit	EMF is measured in Volts (V).	MMF is measured in Ampere-Turns (AT).
Function	In an electric circuit, the electromotive force creates a potential difference between two points and hence causes the current to flow.	In a magnetic circuit, Magnetomotive force establishes the flow of magnetic flux in the core.
Expression	The electromotive force is given by,$\mathrm{EMF\mathit{\, \mathrm{=}\, \frac{W }{Q}}}$ Where, 'W' is the work done and 'Q' is the charge.	The Magnetomotive force is given by the expression, $\mathrm{MMF\mathit{\, \mathrm{=}\, I\cdot N}}$ Where, 'N' is the number of turns and 'I' is the current.
Sources	The sources of EMF are cell, battery, generator, etc.	The sources of MMF are current carrying windings.

Conclusion

EMF and MMF are the key factors responsible for doing work in an electrical circuit and a magnetic circuit, respectively. The key difference that can be pointed out between EMF and MMF is that the EMF causes electric current to flow in an electric circuit, while the MMF causes the flow of magnetic flux in a magnetic circuit.