Magnetic Classification of Materials Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. The phenomenon of perfect diamagnetism is called

1. Zero Kelvin Effect
2. Superconductivity
3. Meissner Effect
4. Diamagnetic Effect

Ans. The correct answer is c. Meissner Effect

Explanation: The Meissner effect refers to the phenomena of perfect diamagnetism in superconductors. It is used to magnetically lift high-speed trains.

Ques. If a material is ferromagnetic, what shall be the value of χ?

1. Large and Positive
2. Negative
3. Small and positive
4. Unit

Ans. The correct answer is a. Large and Positive

Explanation: The magnetic susceptibility χ, of a ferromagnetic material is large and positive. It is negative for diamagnetic materials and small and positive for paramagnetic materials.

Ques. Materials in which magnetization persists even after the field has been removed are called

1. Paramagnetic
2. Hard Ferromagnets
3. Diamagnetic
4. Soft Ferromagnets

Ans. The correct answer is b. Hard Ferromagnets

Explanation: The magnetization of Hard Ferro magnets remains even after the magnetic field is removed. One such material is alnico.

Ques. Which of the following is a diamagnetic material?

1. Calcium
2. Nitrogen (at STP)
3. Sodium
4. Oxygen (at STP)

Ans. The correct answer is b. Nitrogen (at STP)

Explanation: Nitrogen (at STP) is a diamagnetic material. At STP, sodium, calcium, and oxygen are all paramagnetic.

Ques. Which of the following is not a constituent of Alnico?

1. Magnesium
2. Iron
3. Copper
4. Aluminum

Ans. The correct answer is a. Magnesium

Explanation: Alnico is a type of Ferromagnet material. It retains its magnetization long after the field is removed. Iron, aluminum, cobalt, nickel, and copper are its basic constituents.

Ques. Superconductors are diamagnetic materials.

1. True
2. False

Ans. The correct answer is a. True

Explanation: When diamagnetic materials are cooled to extremely low temperatures, they show both perfect conductivity and perfect diamagnetism. The field lines are completely expelled. They are known as superconductors.

Ques. Which among the following is a diamagnetic material?

1. Sodium
2. Cobalt
3. Liquid oxygen
4. Gold

Ans. The correct answer is d. Gold

Explanation: Gold is a diamagnetic material. Diamagnetic materials are repelled by magnets. They have a very weak magnetic field that is opposite to the direction of the applied magnetic field.

Ques. The measure of the magnetization of the material is known as

1. Magnetic stamina
2. Magnetic dipole
3. Magnetic susceptibility
4. None of the above

Ans. The correct answer is c. Magnetic susceptibility

Explanation: Magnetic susceptibility is a measure of magnetization that occurs in the presence of a magnetic field.

Ques. Magnetic materials that align against the magnetic field are known as

1. Ferromagnetic
2. Diamagnetic
3. Paramagnetic
4. None of the above

Ans. The correct answer is b. Diamagnetic

Explanation: Diamagnetic materials align against the magnetic field.

Ques. The capacity of a material to hold on or resist magnetization is known as

1. Retentivity
2. Anti Magnetism
3. Coercivity
4. None of the above

Ans. The correct answer is a. Retentivity

Explanation: The capacity of a substance to resist magnetization is characterized as retentivity.

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Short Answers Questions [2 Marks Questions]

Ques. What are magnetic materials?

Ans. Magnetic materials are substances or materials that are attracted to a magnet. Also, these substances acquire magnetization when attracted to a magnet.

Ques. What are paramagnetic materials?

Ans. Paramagnetic materials are weakly attracted to magnets when placed in a magnetic field. They do not have a permanent magnetic field, but they can be magnetized when placed in a magnetic field. When the magnetic field is removed, the material loses its magnetism.

Ques. What are diamagnetic materials?

Ans. Diamagnetic materials are those that are attracted to a magnetic field. This is due to the induced magnetic field produced by an applied magnetic field in the opposite direction. A magnetic field applied to a material produces a dipole, and the induced dipoles oppose the applied magnetic field. The characteristic of diamagnetic materials is that they have paired electrons.

Ques. What are ferromagnetic materials?

Ans. Ferromagnetic materials have spontaneous net magnetization at the atomic level even in the absence of an external magnetic field. When ferromagnetic materials are subjected to an external magnetic field, they become highly magnetized in the direction of the field.

Ques. What are antiferromagnetic materials?

Ans. Antiferromagnetic materials are materials in which the magnetic moments of the atoms are aligned in an antiparallel fashion. This means that the magnetic moments of neighboring atoms are pointing in opposite directions. This arrangement of magnetic moments results in a net magnetic moment of zero.

Ques. Define retentivity.

Ans. Retentivity, also known as residual magnetism refers to the magnetic induction that remains in the sample after the magnetizing field has been removed.

Ques. Define coercivity.

Ans. Coercivity, also known as magnetic coercivity, coercive field, or coercive force, is a measure of the ability of ferromagnetic material to withstand an external magnetic field without demagnetization.

Ques. What is the Meissner effect?

Ans. The Meissner effect occurs when a superconductor is cooled below its critical temperature, causing a magnetic field to be expelled from it as it enters the superconducting state.

Ques. Define magnetic permeability.

Ans. Magnetic permeability refers to the measure of magnetization that a material produces in response to an applied magnetic field.

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Long Answers Questions [3 Marks Questions]

Ques. What are the different properties of diamagnetic materials?

Ans. The different properties of diamagnetic materials are

• When suspended freely in a uniform magnetic field, diamagnetic materials align themselves perpendicular to the direction of the magnetic field. 
• When suspended freely in a non-uniform magnetic field, they move from the stronger to the weaker part of the magnetic field.
• Diamagnetic materials have a slightly lower relative permeability than unity.
• Their susceptibility is temperature-independent. 
• Diamagnetic materials are always repelled by a magnet.
• The resultant magnetic moment is zero.
• The atomic dipoles in diamagnetic substances are zero since each atom's net magnetic moment is zero due to the existence of paired electrons.

Ques. What is the difference between ferromagnetism and antiferromagnetism?

Ans. The following are the differences between ferromagnetism and antiferromagnetism

Ques. What are the 3 classifications of magnetic materials?

Ans. All materials are divided into three categories based on their magnetic behavior under an external magnetic field. They are

• Diamagnetic materials: When placed in a magnetic field, these materials are weakly magnetized. Magnetic dipoles in these materials tend to align in the opposite direction of the applied field. In effect, they produce an internal magnetic field that resists the applied field, and the material repels the external field that surrounds it.
• Paramagnetic materials: Magnetic dipoles in these magnetic materials tend to align along the applied magnetic field, increasing the applied magnetic field. A magnet will attract such substances if it applies a suitably strong field.
• Ferromagnetic materials: These materials have the strongest magnetic properties. Magnetic dipoles in these materials have been organized into domains with practically perfect arrangements of individual magnetic dipoles, which can produce powerful magnetic fields.

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Very Long Answers Questions [5 Marks Questions]

Ques. A salt contains 2 x 10²³ molecules each having a dipole moment of 1.5 x 10^-22 J/T is kept in a magnetic field of 0.8 T. It is cooled to a temperature of 5 K. It gives a saturation of 20%. What is the magnetic moment of the salt for a magnetic field of 1 T and temperature of 4 K?

Ans. Given

• Number of dipoles, n = 2 x 10²³
• Moment of each dipole, m = 1.5 x 10^-22 J/T
• Degree of saturation, D = 20%

Effective dipole moment, m₁ = 20% of (m x n)

⇒ m₁ = (20/100) x 1.5 x 10^-22 x 2 x 10²³

⇒ m₁ = 6 J T^-1

As per Curie’s law

Magnetic susceptibility, χ = C/T = M/H

⇒ M = CH/T …(i)

Where

• C is Curie’s constant
• T is the absolute temperature
• M is the intensity of magnetization
• H is the intensity of the magnetizing field

But, the intensity of magnetization (M) is directly proportional to the magnetic moment (m). Also, the intensity of the magnetizing field (H) is directly proportional to the magnetic induction (B).

Therefore equation (i), becomes

Magnetic moment, m = CB/T

⇒ m ∝ B/T

⇒ m₂/m₁ = (B₂/B₁) x (T₁/T₂)

⇒ m₂ = m₁ x (B₂/B₁) x (T₁/T₂)

We have, m₁ = 6 J T^-1

Given

• B₁ = 0.8 T
• B₂ = 1 T
• T₁ = 5 K
• T₂ = 4 K

On substituting the values, we get

m₂ = 6 x (1/0.8) x (5/4) = 9.375 J T^-1

Ques. Calculate the permeability and susceptibility of a magnetic bar of cross section 0.4 cm² having a magnetic flux of 4.5 x 10^-5 weber due to magnetic intensity of 6500 A m^-1.

Ans. Given

• Area of the cross-section of the magnetic bar, A = 0.4 cm² = 0.4 x 10^-4 m²
• Magnetic intensity, H = 6500 A m^-1
• Magnetic flux, Φ = 4.5 x 10^-5 weber

Permeability of the magnetic bar is given by

µ = B/ H

Where

• B is the magnetic field
• H is the magnetic intensity

But the magnetic field, B = Φ / A

⇒ µ = Φ / AH

⇒ µ = (4.5 x 10^-5 ) / (0.4 x 10^-4 x 6500) = 1.73 x 10^-4 T m A^-1

Now, magnetic permeability is also given by

µ = µ₀(1 + χ_m)

Where

• µ₀ is the absolute permeability
• χ_m is magnetic susceptibility

⇒ χ_m = (µ/µ₀) - 1

⇒ χ_m = (1.73 x 10^-4 / 4π x 10^-7) - 1

⇒ χ_m = 137

Ques. What is the difference between paramagnetic and diamagnetic materials?

Ans. The following are the differences between paramagnetic and diamagnetic materials

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