Magnetic Materials MCQ Quiz - Objective Question with Answer for Magnetic Materials - Download Free PDF

Explanation:

The magnetic permeability (μ) of a material is related to its magnetic susceptibility (χ_m) as:

μ = μ₀(1 + χ_m)

Where:

• μ = magnetic permeability of the material
• μ₀ = permeability of free space (vacuum)
• χ_m = magnetic susceptibility of the material

This shows a linear relationship between magnetic susceptibility and magnetic permeability for most materials.

However, in many practical magnetic materials, when susceptibility increases significantly, effective permeability may appear to vary inversely in certain contexts like demagnetizing fields or in relative comparisons.

Correct relation: μ = μ₀(1 + χ_m) ⇒ linear relation

Ans.(4)

Sol.

A. In the absence of an external magnetic field, the net magnetic moment of diamagnetic substance is zero

E. Susceptibility of Diamagnetic, χ < 0

Ans.(2)

Sol.

For diamagnetic material, χ < 0

It is diamagnetic material.

Concept:

Ferromagnetic materials are chosen for transformer cores due to their ability to enhance magnetic flux linkage. These materials should ideally possess high permeability to ensure efficient magnetization and low hysteresis loss to minimize energy dissipation.

Explanation: 

Permeability refers to the ability of a material to support the formation of a magnetic field within itself. A high permeability material allows magnetic lines of force to pass through it more easily, which is crucial for efficient transformer operation.

Hysteresis loss is the energy lost in the form of heat when the material undergoes cyclic magnetization and demagnetization. Low hysteresis loss is desirable in transformer cores to reduce energy loss and improve efficiency.

Therefore, the ferromagnetic material used in transformers must have high permeability and low hysteresis loss.

The correct option is (2).

Concept:

• Diamagnetic Substances are substances that acquire feeble magnetism when placed in a magnetic field and the direction of the induced magnetic field is opposite to that of the applied magnetic field. Examples are bismuth, copper, silver, gold, mercury etc. 
• Paramagnetic Substances are substances that acquire feeble magnetism when placed in a magnetic field and the direction of the induced magnetic field is the same as that of the applied magnetic field. Examples are aluminium, manganese, platinum etc. 
• Ferromagnetic substances are substances that acquire strong magnetism when placed in a magnetic field and the direction of the induced magnetic field is same as that of the applied magnetic field. Examples are iron, cobalt, nickel etc. 
• Ferrimagnetic Substances: This effect is observed when the magnetic moments of the domains in the substance are aligned in parallel and anti-parallel directions in unequal numbers. Ferrimagnetic substances are weakly attracted by a magnetic field as compared to ferromagnetic substances. Example: NiFe2O4, CoFe2O4, Fe3O4 (or FeO.Fe2O3), CuFe2O4 etc.

Explanation:

• Ferromagnetic metals are strongly attracted by a magnetic force.
• The common ferromagnetic metals include iron, nickel, cobalt and alloys such as steel.
• Ferromagnetic metals are commonly used to make permanent magnets.

Concept:

Magnet: It is defined as a material that can produce its own magnetic field. There are two types of magnet,

• Permanent magnet
• Temporary magnet

Permanent magnet: These magnets do not lose their magnetic property once they are magnetized. For example alnico, samarium cobalt, ferrite.

Temporary magnet: These magnets act like permanent magnets only when they are within a strong magnetic field. It is made up of soft iron. for example electromagnet.

Alnico:

• The alloy which are permanent magnets that are primarily made up of a combination of aluminium, nickel and cobalt but can also include copper, iron and titanium.
• It can be easily magnetized in an external magnetic field.
• Due to its high coercivity and low retentivity, ​it will not lose its magnetic property.
• It has excellent temperature stability.

Explanation:

• Aluminum behaves like a very weak magnet. When exposed to permanent magnets, paramagnetic materials are weakly attracted.
• Soft iron does not retain magnetism permanently, therefore soft iron core is used in electromagnets.
• Copper is not magnetic itself. We can't observe it without very large magnetic fields.

From the above discussion, we can conclude that alnico is the best material to make a permanent magnet.

CONCEPT:

Diamagnetic Substance:

• Diamagnetic substances are those which develop feeble magnetization in the opposite direction of the magnetizing field.
• Such substances are feebly repelled by magnets and tend to move from stronger to weaker parts of a magnetic field.
• Magnetic susceptibility is small and negative i.e. -1 ≤  χ ≤ 0.
• Examples: Bismuth, copper, lead, zinc, etc.

Paramagnetic substances:

• Paramagnetic substances are those which develop feeble magnetization in the direction of the magnetizing field.
• Such substances are feebly attracted by magnets and tend to move from weaker to stronger parts of a magnetic field. Therefore option 2 is incorrect.
• Magnetic susceptibility is small and positive i.e. 0<  χ.
• Example: Manganese, aluminum, chromium, platinum, etc.

Ferromagnetic substances:

• Ferromagnetic substances are those which develop strong magnetization in the direction of the magnetizing field.
• They are strongly attracted by a magnet and tend to move from weaker to the stronger part of a magnetic field.
• Magnetic susceptibility is very large and positive i.e. χ > 1000.
• Example: Iron, cobalt, nickel, gadolinium, and alloys like alnico.

EXPLANATION:

• From the above options, only wood does not have unpaired electron spins that can line up with a magnet, and so it is a non-magnetic material.

CONCEPT:

• Magnetic permeability: The ratio of the magnetic induction (B) to the magnetic intensity (H) is defined as magnetic permeability.
  • Magnetic permeability is usually defined by the Greek letter μ (Italicized).
  • This is the degree of magnetization produced by a material in response to an applied magnetic field

The formula of magnetic permeability is given by:

μ  = B/H

• Magnetic reluctivity: The reciprocal permeability of magnets is called magnetic reluctivity.
• The intensity of Magnetisation: The moment of the magnetic dipole formed per unit volume when a magnetic material undergoes the magnetization field is called the intensity of magnetization.
• Magnetic susceptibility: The ratio of the intensity of magnetization to magnetic intensity is defined as the Magnetic Susceptibility.

​EXPLANATION:

• The ratio of the magnetic induction to the magnetic intensity is defined as magnetic permeability. So option 4 is correct.

CONCEPT:

• Magnetic susceptibility (χm): It is the property of the substance which shows how easily a substance can be magnetized.
• It is defined as the ratio of the intensity of magnetization (M) in a substance to the magnetic intensity (H) applied to the substance,  i.e. \(\chi = \frac{M}{H}\)
• It is a scalar quantity with no units and dimensions. 
• Magnetic permeability (μ): It is the degree or extent to which magnetic lines of force can enter a substance.

EXPLANATION:

The relation between permeability and susceptibility: Total magnetic flux density B in a material is the sum of magnetic flux density in vacuum Bo produced by magnetizing force and magnetic flux density due to magnetization of the material Bm 

​i.e.,B = Bo + B_m

Using the above equation we can derive the relative magnetic permeability of material as

⇒ μr = 1 + χ

Hence, option 3 is correct.

Extra point:

The above derivation can be expressed as

 B = Bo + Bm ⇒ B = μ₀H + μ₀M = μ₀H (1 + χ) 

μ_r = 1 + χ   (∵ μ_r = B/H ) 

Concept:

Magnetic field lines: The imaginary lines which represent the direction of the magnetic field are called magnetic field lines.

The characteristics of the magnetic lines of force are as follows:

1. They are closed curves. Outside the magnet, they are from north to south pole whereas, inside the magnet, it is the other way round. 
2. If the lines of force are crowded at a place, the field is strong. 
3. If the lines of force are parallel and equidistant, the concerned magnetic field will be uniform in nature. 
4. Two magnetic lines of force will near intersect each other.
5. The tangent at any point on the field lines gives the direction of the magnetic field vector at that point.
6. Magnetic monopoles do not exist.

Magnetic Susceptibility: The measurement of how much a magnetic material will get magnetized in a magnetic field is called susceptibility. It is denoted by χ.

Ferromagnetic materials: The material which exhibits strong magnetism in a magnetic field in the direction of the magnetic field is called a ferromagnetic substance.

χ ≫ 1 for ferromagnetic substance.

Permeability (μ0): The measurement of the ability of any material which allows the formation of magnetic lines of force is called permeability.

It is a scalar quantity.

​Explanation:

1. Magnetic field lines form closed loops. So statement 1 is wrong.
2. Magnetic monopoles do not exist. So statement 2 is correct.
3. Ferromagnetic materials have large magnetic susceptibility (χ ≫ 1). So statement 3 is correct.
4. The permeability of free space is a scalar quantity. So statement 4 is correct.

Concept:

• The measurement of how much a magnetic material will get magnetized in a magnetic field is called susceptibility.
• It is denoted by χ.
• Magnetic susceptibility is the ratio of magnetization and the applied magnetizing field intensity. 
• Magnetic Susceptibility (χ) = Magnetization/magnetizing field intensity
• The material which exhibits strong magnetism in a magnetic field in the direction of the magnetic field is called a ferromagnetic substance.
• The magnetic materials which are weekly attracted by a magnet are called a paramagnetic substance.
• The magnetic material which is repelled by a magnet is called diamagnetic material.

Explanation:

• As ferromagnetic materials exhibit strong magnetism in a magnetic field. So the susceptibility of ferromagnetic is much greater than 1.
• Hence option 1 is correct among all

Extra Points:

These are susceptibility of different materials

χ ≫ 1 for ferromagnetic substance. 

χ > 0 for paramagnetic substance

CONCEPT:

• The measurement of how much a magnetic material will get magnetized in a magnetic field is called susceptibility. It is denoted by χ.
• Magnetic susceptibility is the ratio of magnetization and the applied magnetizing field intensity.

\(Magnetic\;Susceptibility\;\left( \chi \right) = \frac{{Magnetization\;\left( M \right)}}{{magnetizing\;field\;intensity\;\left( H \right)}}\)

EXPLANATION:

1. The product of the strength of pole and effective length is called a magnetic moment.
2. The ratio of permeability of a medium to the permeability of free space is called relative magnetic permeability.
3. The total magnetic field passing through a surface area normally is called magnetic flux.
4. M/H is equal to magnetic susceptibility. So option 4 is correct.

CONCEPT:

Intensity of magnetization:

• When a magnetic material is placed in a magnetizing field, it gets magnetized.
• The magnetic moment developed per unit volume of a material when placed in a magnetizing field is called intensity of magnetization or simply magnetization. Thus

​\(\vec M = \frac{{\vec m}}{V}\)
Or,
BM = μonIM = μoM

EXPLANATION:

• Magnetic susceptibility is defined as the ratio of the intensity of magnetization (I) in a substance to the magnetic intensity (H) applied to the substance, i.e. \(\chi = \frac{I}{H}\). Therefore option 1 is incorrect.

• A magnetic moment or magnetic dipole moment (M) represents the strength of a magnet.  it is defined as the product of the strength of either pole or effective length. Therefore option 2 is incorrect.

• From above it is clear that B/μo = M is the magnetic intensity. Therefore option 3 is correct.

• Magnetic Flux (Φ) is defined as the total number of magnetic lines of force passing normally through an area placed in a magnetic field is equal to the magnetic flux linked with that area.

Hard ferrites have high coercivity, so are difficult to demagnetize. They are used to make light weight permanent magnets for applications such as refrigerator magnets, loudspeakers, and small electric motors.

Soft ferrites have low coercivity, so they easily change their magnetization and act as conductors of magnetic fields. They are used in the electronics industry to make efficient magnetic cores called ferrite cores for high-frequency inductors, transformers and antennas, and in various microwave components.