A magnetic pressure which sets up or tends to set up flux in a magnetic circuit is called-
Magnetomotive force
Understanding Magnetomotive Force in Magnetic Circuits
The question asks to identify the term for the "magnetic pressure" that establishes or tends to establish magnetic flux within a magnetic circuit. Let's break down the concepts and options provided.
What is a Magnetic Circuit?
A magnetic circuit is a path for magnetic flux, usually made of ferromagnetic materials, where the magnetic field lines are largely confined. Just like an electric circuit has a source of electromotive force (EMF) that drives electric current, a magnetic circuit has a source of magnetomotive force (MMF) that drives magnetic flux.
Analyzing the Options
Let's look at each option:
- Magnetomotive force (MMF): This is defined as the property of certain circuits (magnetic circuits) to produce magnetic flux. It is the "force" that sets up the magnetic field and flux lines in a magnetic circuit, analogous to voltage (EMF) in an electric circuit which drives current. MMF is typically created by a current flowing through a coil of wire and is measured in Ampere-turns (AT). The formula for MMF is given by:
\( \mathcal{F} = NI \)
where \( \mathcal{F} \) is the MMF, \( N \) is the number of turns in the coil, and \( I \) is the current flowing through the coil. - Magnetic field: This refers to the region around a magnetic material or a current-carrying conductor where magnetic forces can be detected. It is often described by magnetic field strength (H) or magnetic flux density (B). While related to flux, it is not the driving force that *sets up* the flux in the entire circuit.
- Cross magnetisation: This term is usually used in the context of electrical machines (like DC machines) and refers to the distorting effect of the armature reaction field on the main field, specifically across the main pole axis. It is not the fundamental force that establishes flux in a magnetic circuit.
- Demagnetisation: This is the process of removing the magnetic properties from a material. It is the opposite of establishing magnetization or flux.
Connecting to the Question
The question describes a "magnetic pressure which sets up or tends to set up flux". This description perfectly matches the definition and function of Magnetomotive force (MMF). It is the driving force behind the magnetic flux in a magnetic circuit, analogous to how EMF drives current in an electric circuit.
| Electric Circuit | Magnetic Circuit |
|---|---|
| Electromotive Force (EMF), V | Magnetomotive Force (MMF), \( \mathcal{F} \) |
| Current, I | Magnetic Flux, \( \Phi \) |
| Resistance, R | Reluctance, \( \mathcal{R} \) |
| Ohm's Law: \( V = IR \) | Hopkinson's Law (Magnetic Ohm's Law): \( \mathcal{F} = \Phi \mathcal{R} \) |
Based on this analogy and the definitions, the term that represents the magnetic pressure setting up flux is Magnetomotive force.
Revision Table: Key Concepts Revisited
| Term | Role in Magnetic Circuit | Analogy in Electric Circuit |
|---|---|---|
| Magnetomotive Force (MMF) | Driving force that sets up flux | Electromotive Force (EMF) |
| Magnetic Flux | The quantity set up by MMF | Electric Current |
| Reluctance | Opposition to flux | Resistance |
Additional Information: Magnetic Circuit Elements
Just like an electric circuit can be analyzed using concepts like voltage, current, and resistance, a magnetic circuit uses MMF, flux, and reluctance.
- Reluctance (\( \mathcal{R} \)): This is the opposition offered by a magnetic circuit to the magnetic flux. It is analogous to resistance in an electric circuit. Reluctance depends on the material properties (permeability) and the dimensions (length and cross-sectional area) of the magnetic path. The formula for reluctance is \( \mathcal{R} = \frac{l}{\mu A} \), where \( l \) is the mean length, \( \mu \) is the permeability, and \( A \) is the cross-sectional area.
- Permeability (\( \mu \)): This is a measure of how easily a material can support the formation of a magnetic field within itself. It is analogous to conductivity in an electric circuit (which is the reciprocal of resistivity). High permeability means low reluctance.
Understanding these analogies helps in analyzing complex magnetic circuits, similar to how electric circuits are analyzed using Ohm's Law and Kirchhoff's Laws.
Important Questions from Magnetostatics
A coil of 600 turns and of resistance of 20 Ω is wound uniformly over a steel ring of mean circumference 30 cm and cross sectional area 9 cm2. If the relative permeability of the ring is 1600. Find the value of reluctance.
The unit of magnetic flux density is
The B-H curve for ______ will be a straight line passing through the origin.
The SI unit of permeability is:
Which of the following equations accurately describes the relationship between the magnetic flux density ($B$) and the magnetic field strength ($H$) in a homogeneous isotropic material, given its absolute permeability ($\mu$)?
