How Does Magnetomotive Force Affect Magnetic Circuits?
Before we are going to start about “what is mmf”,magnetomotive force and its unit. First, we must have the knowledge regarding the magnetic circuit and various terms related to it like magnetic reluctance, magnetic flux etc. Therefore first we are going to study magnetic circuits. A magnetic field, shown as lines of magnetic flux, is restricted to a magnetic circuit, which is a closed channel. In contrast to an electric circuit, where electricity flows, a magnetic circuit has no electricity flowing through it. The magnetic field or flux in a ring-shaped electromagnet with a tiny air gap is nearly totally contained to the metal core and the air gap, which together form the magnetic circuit.
(Image will be Uploaded soon)
The magnetic field of an electric motor is restricted mostly to the magnetic pole pieces, the rotor, the air gaps between the rotor and the pole pieces, and the metal frame. Each magnetic field line forms an uninterrupted circle. The total flux is the sum of all the lines. The magnetic circuit is considered parallel when the flux is split so that part of it is limited to one section of the device and the other to another. A series magnetic circuit is formed when all of the flux is contained within a single closed loop, as in a ring-shaped electromagnet. The current, electromotive force (voltage), and resistance are all related by Ohm's equation in a magnetic circuit, just as they are in an electric circuit.
What is MMF?
The electric current is equivalent to the magnetic flux. The magnetomotive force, abbreviated as mmf, is comparable to the electromotive force and may be thought of as the flux-setting factor. The mmf is measured in ampere-turns and is comparable to the number of turns of wire carrying an electric current.The mmf rises as the current through a coil (as in an electromagnet) or the number of turns of wire in the coil is increased, and the magnetic flux increases accordingly if the remainder of the magnetic circuit stays unchanged. A magnetic circuit's reluctance is similar to an electric circuit's resistance. Reluctance is determined by the geometric and material aspects of the circuit that provide resistance to the presence of magnetic flux.
A given component of a magnetic circuit's reluctance is related to its length and inversely proportional to its cross-sectional area and permeability, a magnetic property of the supplied material. Iron, for example, has a very high permeability in comparison to air, therefore it has a very low reluctance, or gives very little resistance to the presence of magnetic flux. In a series magnetic circuit, the total reluctance is the sum of the individual reluctances encountered around the closed flux channel.
Magnetomotive Force Definition
The presence of electromotive force causes current to flow in an electric circuit, while the presence of magnetomotive force (MMF) causes magnetic flux to flow in a magnetic circuit. Magnetomotive Force is the magnetic pressure that creates the magnetic flux in a magnetic circuit. The SI unit of magnetomotive force is ampere - turn (AT) and in CGS system is G (gilbert). The MMF for the inductive coil seen in the diagram below is,
(Image will be Uploaded soon)
The product of the current around the turns and the number of turns in the coil equals the MMF's strength. Under work law, MMF is defined as the force required to move the unit's magnetic pole once around the magnetic circuit. Therefore, the magnetomotive force formula is expressed as,
Fm = NI
Here, Fm is the magnetomotive force, N is the number of turns and I is the current flowing through a coil.
The magnetic potential is another name for the MMF. It is the property of a substance that causes a magnetic field to form. The product of magnetic flux and magnetic reluctance is used to compute the magnetomotive force. The resistance is the magnetic field's opposition to establishing the magnetic flux on it. The reluctance and magnetic flux MMF is given as,
Fm = ФR
Here, Ф is the magnetic flux and R is the reluctance of a circuit.
The magnetomotive force may be measured in terms of magnetic field intensity and material length. The magnetic field strength is the force acting on the magnetic field's unit pole. The MMF for field intensity is stated as,
Fm=Hl
Here, H is the magnetic field intensity and l is the material length.
FAQs on Magnetomotive Force Explained with Examples
1. What is Magnetomotive Force (MMF) in physics?
Magnetomotive Force, abbreviated as MMF, is the force that establishes magnetic flux in a magnetic circuit. It is analogous to the Electromotive Force (EMF) in an electrical circuit, which drives the flow of electric current. In simple terms, MMF is the flux-producing capability of an electric current flowing through a coil.
2. How do you calculate Magnetomotive Force using its formula?
The Magnetomotive Force (MMF) is calculated using the formula: Fm = N × I. In this equation:
- Fm is the magnetomotive force.
- N represents the total number of turns or windings in the coil.
- I is the electric current in amperes flowing through the coil.
3. What are the standard SI and CGS units of Magnetomotive Force?
The units for Magnetomotive Force differ between measurement systems:
- The SI unit for MMF is the Ampere-turn (At).
- The CGS (Centimetre-Gram-Second) unit for MMF is the Gilbert (Gb).
4. How are Magnetomotive Force (MMF), magnetic flux, and reluctance related?
The relationship between Magnetomotive Force (Fm), magnetic flux (Φ), and reluctance (ℜ) in a magnetic circuit is described by Hopkinson's Law, which is the magnetic equivalent of Ohm's Law. The formula is Fm = Φ × ℜ. This means the MMF is the product of the magnetic flux and the reluctance of the circuit, just as voltage (EMF) is the product of current and resistance in an electrical circuit.
5. What is a key difference between Magnetomotive Force and Electromotive Force (EMF)?
The key difference lies in what they produce and the opposition they overcome. Electromotive Force (EMF) drives electric current (flow of charge) through a circuit, overcoming electrical resistance. In contrast, Magnetomotive Force (MMF) drives magnetic flux (magnetic field lines) through a magnetic circuit, overcoming magnetic reluctance. Unlike electrical resistance, reluctance does not cause energy dissipation as heat.
6. Why is an air gap sometimes intentionally created in a magnetic circuit?
An air gap is intentionally introduced into a magnetic circuit, such as in an inductor or electromagnet, to increase the circuit's overall magnetic reluctance. While this reduces the magnetic flux for a given MMF, it serves a crucial purpose: it prevents the magnetic core material from reaching saturation too quickly. This allows the device to handle higher currents and store more energy in its magnetic field before its performance degrades.
7. Provide a practical example where the principle of Magnetomotive Force is applied.
A classic example is in a transformer. The primary winding of a transformer has a specific number of turns (N) and is supplied with an alternating current (I). This combination creates a Magnetomotive Force (MMF = N × I) that generates an alternating magnetic flux within the iron core. This flux then induces an EMF in the secondary winding, demonstrating how MMF is fundamental to the operation of transformers, motors, and generators.
