Magnetism and Magnetic Materials Quiz
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Questions and Answers

What happens to the magnetic field (B) when the applied field (H) is gradually decreased and brought back to zero?

  • The field B follows a different curve than its original path, and the material remains magnetized. (correct)
  • The field B retraces its original path, returning to zero.
  • The field B fluctuates and remains magnetized at a value of B, but not permanently
  • The field B becomes permanently magnetized at a value of B.

When the applied magnetic field is reversed, what happens to the magnetic moments in the material?

  • They become randomly aligned, resulting in a complete loss of magnetization.
  • They continue to align in the same direction but with a reduced magnitude.
  • They remain aligned in the same direction as the initial applied field.
  • They align opposite to the initial applied field, resulting in the reduction of the magnetic field. (correct)

What is the characteristic of a material suitable for a permanent magnet?

  • A broad hysteresis loop with high retentivity and coercive force (correct)
  • A broad hysteresis loop with low retentivity and coercive force
  • A narrow hysteresis loop with high retentivity and coercive force
  • A narrow hysteresis loop with low retentivity and coercive force

What is the definition of remanence or retentivity?

<p>The magnetic field that remains after the material is saturated and the applied field is reduced to zero (D)</p> Signup and view all the answers

What is the significance of hysteresis loss in a ferromagnetic material?

<p>It indicates the amount of energy lost as heat during each magnetization cycle. (A)</p> Signup and view all the answers

What is the definition of coercivity?

<p>The magnetic field required to completely demagnetize the material (C)</p> Signup and view all the answers

What is the relationship between the shape of the hysteresis loop and the material's magnetic properties?

<p>The larger the area of the hysteresis loop, the better the material is for a permanent magnet. (A)</p> Signup and view all the answers

What does it mean for the permeability of a ferromagnetic material to vary with the applied field and the history of the material?

<p>The material's magnetic properties are dependent on the applied field and its previous magnetization state. (A)</p> Signup and view all the answers

What behavior characterizes diamagnetic materials in a magnetic field?

<p>They are repelled by magnets. (A)</p> Signup and view all the answers

In what direction do diamagnetic materials acquire induced dipole moments when subjected to an external magnetic field?

<p>In the opposite direction to the applied field. (A)</p> Signup and view all the answers

Which of the following is a property of paramagnetic materials?

<p>They are weakly attracted by magnets. (D)</p> Signup and view all the answers

What happens to a paramagnetic rod when freely suspended in a magnetic field?

<p>It aligns along the direction of the applied field. (D)</p> Signup and view all the answers

Which material does NOT exhibit diamagnetic properties?

<p>Oxygen (B)</p> Signup and view all the answers

What value does the magnetic susceptibility of diamagnetic materials typically take?

<p>Negative values ranging from -10 to -10. (D)</p> Signup and view all the answers

What is a characteristic of the relative permeability of paramagnetic materials?

<p>It ranges from approximately 1.00001 to 1.003. (A)</p> Signup and view all the answers

How do diamagnetic materials behave in a magnetic field compared to paramagnetic materials?

<p>Diamagnetic materials are repelled, while paramagnetic materials are attracted. (C)</p> Signup and view all the answers

What produces the magnetic moment of an electron due to its orbital motion?

<p>The electron's charge and its orbit (A)</p> Signup and view all the answers

What happens to the current loops in a material when an external magnetic field is applied?

<p>They get oriented in a specific direction (C)</p> Signup and view all the answers

How is the intensity of magnetization defined?

<p>As the total magnetic moment divided by the volume (B)</p> Signup and view all the answers

What is the unit of the intensity of magnetization?

<p>Ampere per meter (B)</p> Signup and view all the answers

Which of the following describes magnetic permeability?

<p>The ratio of magnetic field inside a material to the magnetizing field intensity (D)</p> Signup and view all the answers

What is relative permeability a measure of?

<p>The permeability of a material compared to that of free space (C)</p> Signup and view all the answers

What is the net magnetic moment of a material composed of?

<p>The vector sum of all magnetic moments of the electrons (B)</p> Signup and view all the answers

Which of the following statements about magnetization is FALSE?

<p>A magnet cannot be magnetized by an external field (B)</p> Signup and view all the answers

What is the relationship between magnetic susceptibility (𝜒) and intensity of magnetization (𝐼)?

<p>𝜒 = 𝐼 / 𝐻 (A)</p> Signup and view all the answers

Which formula correctly describes the relationship between the magnetic field (𝐵), magnetizing field intensity (𝐻), and intensity of magnetization (𝐼)?

<p>𝐵 = 𝜇(𝐻) + 𝜇(𝐼) (A)</p> Signup and view all the answers

What does the term 𝜇 represent in the context of magnetism?

<p>Permeability of free space (B)</p> Signup and view all the answers

What does the equation 𝜇 = 𝜇(1 + 𝜒) represent?

<p>Relation between permeability and relative permeability (A)</p> Signup and view all the answers

When an iron rod is placed inside a magnetic field, what is primarily produced?

<p>A magnetic field due to its own induced dipoles (A)</p> Signup and view all the answers

In the context of solenoids, how is the magnetizing field intensity (𝐻) expressed?

<p>𝐻 = n𝐼 (B)</p> Signup and view all the answers

What does the classification of magnetic materials depend on?

<p>Responses to an external magnetic field (C)</p> Signup and view all the answers

What signifies a unitless quantity in magnetism among the terms discussed?

<p>Magnetic susceptibility (𝜒) (C)</p> Signup and view all the answers

What happens to the magnetic susceptibility of paramagnetic materials as temperature increases?

<p>It is inversely proportional to the absolute temperature. (B)</p> Signup and view all the answers

Which of the following materials is NOT classified as a ferromagnetic material?

<p>Copper (A)</p> Signup and view all the answers

What is the Curie temperature?

<p>The temperature at which a ferromagnetic material becomes paramagnetic. (C)</p> Signup and view all the answers

What is the relationship between intensity of magnetization and temperature for paramagnetic materials?

<p>It decreases with increasing temperature. (C)</p> Signup and view all the answers

Which property is characteristic of ferromagnetic materials?

<p>They can be easily magnetized by a magnetic field. (D)</p> Signup and view all the answers

How does the magnetic susceptibility of ferromagnetic materials change with applied magnetic field?

<p>It varies and can become very high. (B)</p> Signup and view all the answers

What happens to magnetic domains in a ferromagnetic material when it is placed in an external magnetic field?

<p>They tend to align with the field direction. (B)</p> Signup and view all the answers

What role does the Curie constant (C) play in the formula for magnetic susceptibility?

<p>It provides a measure of the degree of magnetization for different materials. (B)</p> Signup and view all the answers

What results from the presence of multiple magnetic domains in a ferromagnetic substance when no external magnetic field is applied?

<p>The net magnetic moment is zero due to random orientations. (B)</p> Signup and view all the answers

What effect does temperature have on the alignment of atomic moments in ferromagnetic materials?

<p>Increased temperature disturbs alignment. (C)</p> Signup and view all the answers

What does a ferromagnetic material exhibit when it reaches magnetic saturation?

<p>Magnetization remains constant despite further increases in the applied field. (A)</p> Signup and view all the answers

What role does thermal motion at room temperature play in the orientation of atomic magnetic moments in ferromagnetic materials?

<p>It has no effect on the specific orientation. (A)</p> Signup and view all the answers

In the hysteresis loop for a ferromagnetic material, what happens when the applied magnetic field is removed after reaching saturation?

<p>The material retains some level of magnetization. (C)</p> Signup and view all the answers

Which statement best describes what occurs in a ferromagnetic material under a weak external magnetic field?

<p>Some domains begin to orient along the field direction. (B)</p> Signup and view all the answers

What is the effect of increased strength of an external magnetic field on the dimensions of magnetic domains in a ferromagnetic material?

<p>Domains not aligned with the field shrink. (D)</p> Signup and view all the answers

In the context of ferromagnetism, what defines a magnetic domain?

<p>A region where atomic magnetic moments are aligned in the same direction. (A)</p> Signup and view all the answers

Flashcards

Magnetic Permeability

The ability of a material to become magnetized when exposed to an external magnetic field.

Magnetic Field Intensity (H)

The strength of a magnetic field inside a material.

Intensity of Magnetization (I)

The net magnetic dipole moment per unit volume of a material.

Relative Permeability (μr)

The ratio of the magnetic permeability of a material to the magnetic permeability of free space.

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Spin Magnetic Moment

The magnetic moment created by the spinning of an electron.

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Orbital Magnetic Moment

The magnetic moment created by an electron's orbital motion around the nucleus.

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Net Magnetic Moment of an Atom

The magnetic moment of an atom is the vector sum of the orbital and spin magnetic moments of its electrons.

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Diamagnetic Materials

Materials that exhibit weak magnetic properties and are not easily magnetized.

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Magnetic Susceptibility (𝜒)

A unitless quantity that describes how easily a material can be magnetized by an external magnetic field.

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What is the formula for magnetic susceptibility?

The ratio of the intensity of magnetization (I) to the magnetizing field intensity (H).

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Magnetization Field (𝐵)

The magnetic field produced by the alignment of magnetic dipoles within a material.

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What is the relationship between the applied magnetic field, magnetization field, and the total magnetic field inside a material?

The total magnetic field inside a material, which is the sum of the applied magnetic field and the magnetization field.

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Relative Permeability (𝜇r)

The ratio of the magnetic permeability of a material to the permeability of free space.

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Magnetic Permeability (𝜇)

The ability of a material to become magnetized when exposed to an external magnetic field.

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What is a ferromagnetic material?

A material with a relative permeability greater than 1. It is easily magnetized and attracts magnetic fields strongly.

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What is a diamagnetic material?

A material with a relative permeability less than 1. It is weakly magnetized and repelled by magnetic fields.

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Paramagnetic material

A material that is weakly magnetized in the same direction as an applied magnetic field. It is attracted by magnets.

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What are Ferromagnetic Materials?

Materials that are strongly attracted by a magnet. They are highly magnetized in a magnetic field. Examples include iron, nickel, cobalt, and their alloys.

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What is the Curie Temperature?

The temperature at which a ferromagnetic material loses its magnetic properties and becomes paramagnetic. This happens because the thermal vibrations disrupt the alignment of atomic magnetic moments.

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What is Curie's Law?

The relationship between the intensity of magnetization (I) and the absolute temperature (T) in paramagnetic materials. It states that the intensity of magnetization is inversely proportional to the absolute temperature.

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What is Magnetic Susceptibility (χ) for Paramagnetic Materials?

A property of paramagnetic materials that reflects how easily they become magnetized in a magnetic field. It's small and positive, meaning they are weakly attracted by magnets.

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What is the Relative Permeability of Ferromagnetic Materials?

Ferromagnetic materials have a very high relative permeability, typically in the range of 1000 to 100,000. This means they are highly permeable to magnetic fields and can easily become magnetized.

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What is the Alignment of Atomic Magnetic Moments in Ferromagnetic Materials?

The net alignment of the magnetic moments of atoms in a ferromagnetic material. It can be disturbed by increasing temperature, leading to a decrease in magnetic properties.

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What is the Magnetic Susceptibility of Ferromagnetic Materials?

Ferromagnetic materials exhibit positive and very high magnetic susceptibility. This means they are strongly attracted by magnets and easily become magnetized.

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What does the Ferromagnetic Property Depend on?

Ferromagnetic property is only observed in solid materials. It does not exist in liquids or gases.

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Magnetic Domains

Tiny regions within a ferromagnetic material where atomic magnetic moments align parallel to each other, creating a strong localized magnetic field.

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Hysteresis

The phenomenon where the magnetization of a ferromagnetic material lags behind the applied magnetic field, resulting in a hysteresis loop.

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Magnetic Saturation

The maximum magnetization that a ferromagnetic material can achieve when exposed to an applied magnetic field. This occurs when all the magnetic moments in the material are aligned.

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Random Domain Orientation (Zero Net Moment)

In the absence of an external magnetic field, magnetic domains in a ferromagnetic substance are randomly oriented, resulting in a net magnetic moment of zero.

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Domain Alignment in an External Field

When a ferromagnetic material is placed in an external magnetic field, the domains tend to align with the field direction. This causes the domain boundaries to shift, and domains aligned with the field grow while others shrink.

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Hysteresis Loop

The magnetization curve of a ferromagnetic material, showing the relationship between the applied magnetic field and the magnetization of the material. It typically exhibits a hysteresis loop.

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Demagnetization

The process of removing an external magnetic field applied to a ferromagnetic material. The magnetization of the material does not completely return to zero, resulting in residual magnetization.

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Remanence (Retentivity)

The magnetic field remaining in a material after the applied field is removed. It's what allows a material like iron to become a permanent magnet.

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Coercivity

The strength of the reverse magnetic field needed to completely demagnetize a material. It indicates how difficult it is to erase the magnetization.

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Permanent Magnet Material

A material with a hysteresis loop that has high values of both remanence and coercivity. It retains its magnetization well and resists demagnetization.

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Soft Magnetic Material

A material with a narrow hysteresis loop, low remanence, and low coercivity. It can be easily magnetized and demagnetized.

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Hysteresis Loop Characteristics

The shape and size of the hysteresis loop are unique to a given material, revealing its magnetic properties and its suitability for different applications.

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Hysteresis Loop Area

The area inside the hysteresis loop represents the energy loss per unit volume during each cycle of magnetization.

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Study Notes

Magnetic Properties of Materials

  • Materials are composed of atoms, and their magnetic properties arise from electron motion (orbital and spin).
  • Each electron possesses an orbital magnetic moment (μ₁) and a spin magnetic moment (μs).
  • The net magnetic moment of an atom (μ) is the vector sum of μ₁ and μs.
  • In many materials, these atomic moments are randomly oriented, cancelling out their magnetic fields.
  • Applying an external magnetic field (magnetizing field) orients the atomic moments in a specific direction, magnetizing the material.

Intensity of Magnetization (I)

  • Intensity of magnetization (I) is the net dipole moment per unit volume of a material with a net magnetic moment (M) in volume (V).
  • I = M/V
  • I is a vector quantity, measured in amperes per meter (Am⁻¹).

Magnetic Permeability (μ)

  • Magnetic permeability (μ) is the ratio of the magnetic flux density (B) inside a material to the magnetizing field intensity (H) within the material.
  • μ = B/H
  • It describes how easily a magnetic field can penetrate a material.

Relative Permeability (μr)

  • Relative permeability (μr) is the ratio of the permeability of a material to the permeability of free space (μ₀).
  • μr = μ/μ₀
  • It's dimensionless and indicates how much a material's permeability differs from that of a vacuum.

Magnetic Susceptibility (χ)

  • Magnetic susceptibility (χ) is the ratio of intensity of magnetization (I) to the magnetizing field intensity (H).
  • χ = I/H
  • It measures how easily a material can be magnetized by an applied magnetic field.
  • It is a dimensionless quantity.

Relation Between μr and χ

  • μr = 1 + χ

Classification of Magnetic Materials

  • Diamagnetic Materials:
    • Weakly repelled by magnets.
    • Magnetic moments are induced in the opposite direction to the applied field.
    • Examples: bismuth, copper, water.
    • Susceptibility is negative (χ < 0) and relatively small.
  • Paramagnetic Materials:
    • Weakly attracted by magnets.
    • Magnetic moments are aligned in the same direction as the applied field, but interactions are weak.
    • Examples: aluminum, oxygen, manganese.
    • Susceptibility is positive (χ > 0) and relatively small. The susceptibility is inversely proportional to temperature.
  • Ferromagnetic Materials:
    • Strongly attracted by magnets.
    • Strong alignment of atomic magnetic moments in the same direction as the applied field, even with no external field.
    • Examples: iron, nickel, cobalt, some alloys.
    • Susceptibility is positive (χ >> 0) and very large. Domain theory explains their behavior.
    • Magnetic properties often depend on temperature and can be a non-linear function of the magnetizing field.

Domain Theory of Ferromagnetism

  • Ferromagnetic materials are composed of many microscopic regions called domains.
  • Within each domain, atomic magnetic moments are aligned.
  • In the absence of an external magnetic field, the domains are randomly oriented, cancelling out the net magnetic moment.
  • An external magnetic field causes the domains to align in the direction of that field, increasing the overall magnetization.

Hysteresis

  • Hysteresis is the lagging of the magnetization behind the applied magnetic field.
  • For the same value of the applied field in either direction, the resulting magnetization does not return to the original value.
  • Hysteresis loops graph the relationship between magnetic field (H) and magnetic flux density (B).
  • The area of the hysteresis loop represents the energy lost per cycle of magnetization (hysteresis loss).
  • A wide/broad hysteresis loop signifies a large energy loss or materials suitable for permanent magnets.
  • A narrow hysteresis loop signifies low energy loss making them suitable for transformer cores (i.e. soft magnetic materials).

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