Content Curator
The magnetic classification of materials is based on the behavior of the materials under the influence of an external magnetic field.
- The magnetic characteristics of a material are determined by how electron clouds organize themselves in atoms and how groupings of these atoms behave.
- The atom or collection of atoms behaves as a magnetic dipole or a small bar magnet that may align in response to a magnetic field.
- The magnetic properties of materials are determined by the overall impact of all these dipoles.
Magnetic materials are classified as
- Diamagnetic materials: These materials are hardly magnetized when placed in the presence of a magnetic field.
- Paramagnetic materials: Magnetic dipoles in paramagnetic materials tend to align along the applied magnetic field, strengthening the applied magnetic field.
- Ferromagnetic materials: When a magnetic field is applied to these materials, it produces an extremely strong magnetism in the direction of the magnetic field.
| Table of Content |
Key Terms: Electromagnets, Magnetic materials, Ferromagnetism, Paramagnetism, Diamagnetism, Electrons, Atoms, Magnetic field, Curie constant, Absolute temperature
What are Magnetic Materials?
[Click Here for Sample Questions]
Magnetic materials are substances or materials that are attracted to a magnet.
- At some point, every material exhibits magnetic behavior.
- This magnetic behavior is due to the reason that these substances are made up of charged particles such as electrons and protons.
- The magnetic characteristics of a material are determined by how electrons are grouped in atoms and how groups of these atoms behave.
- As a result, these atoms (or groups of atoms) form a magnetic dipole or a small magnet that may align depending on the magnetic field applied.
- The magnetic characteristics of magnetic materials are determined by the resultant influence of these dipoles.
Properties of Magnetic Materials
Do check out:
| Chapter Related Links | ||
|---|---|---|
| SI unit of magnetic field | Poles of magnets | Einstein Field Equation |
| Difference between electromagnet and permanent magnet | Magnetic Declination | Magnetometer |
Magnetic Classification of Materials
[Click Here for Previous Year Questions]
All materials are classified into three classes according to their magnetic behavior when placed in an external magnetic field. They are
Diamagnetic materials
The materials that are weakly magnetized in a direction opposite to the applied magnetic field are known as diamagnetic materials.
- It is very difficult to magnetize a diamagnetic material.
- They require a very strong magnetic field to show magnetic properties.
- Some examples of diamagnetic materials are gold, silver, copper, zinc, water, alcohol, argon, air, etc.
Magnetic field lines through diamagnetic materials
Paramagnetic materials
The materials that are weakly magnetized in the direction of the applied magnetic field are known as paramagnetic materials.
Some examples of paramagnetic materials are aluminum, chromium, platinum, sodium, lithium, etc.
Ferromagnetic materials
The materials that are strongly magnetized in the presence of an applied magnetic field are known as Ferromagnetic materials.
- The ferromagnetic effect is noticed even in the presence of a weak magnetic field. With the rise in temperature, it becomes comparatively less easy to magnetize the ferromagnetic substance.
- Some examples of ferromagnetic materials are iron, steel, nickel, cobalt, etc.
Properties of Magnetic Materials
[Click Here for Sample Questions]
The different properties of magnetic materials are shown in the table below
| Ferromagnetic Materials | Paramagnetic Materials | Diamagnetic Materials |
|---|---|---|
| They are strongly attracted by a magnet. | They are weakly attracted by a magnet. | They are weakly repelled by a magnet. |
| A freely suspended ferromagnetic rod quickly sets itself along the direction of the external electric field. | A freely suspended paramagnetic rod slowly sets itself along the direction of the external electric field. | A freely suspended diamagnetic rod slowly sets itself at a right angle to the direction of the external electric field. |
| When they are placed in a magnetic field, the magnetic field lines prefer to pass through them. | When they are placed in a magnetic field, most of the magnetic field lines prefer to pass through them. | When they are placed in a magnetic field, the magnetic field lines do not prefer to pass through them. |
| Magnetic field induction within the sample is much more than the magnetic intensity. | Magnetic field induction within the sample is much more than the magnetic intensity. | Magnetic field induction within the sample is less than the magnetic intensity. |
| Permeability is much more than unity. | Permeability is more than unity. | Permeability is less than unity. |
| Magnetic flux density inside a ferromagnetic material is much larger than in air. | Magnetic flux density inside a paramagnetic material is larger than in air. | Magnetic flux density inside a diamagnetic material is less than in air. |
Curie’s Law in Paramagnetism
[Click Here for Previous Year Questions]
Curie’s law states that the magnetization of paramagnetic material is inversely proportional to the absolute temperature of the material.
In other words, magnetic susceptibility χ of a paramagnetic material is inversely proportional to the absolute temperature T of the material.
It is experimentally found that the magnetization of the paramagnetic substance is given by
M = CB0/T
Where
- C is Curie's constant
- T is the absolute temperature
Since, B0 = µ0H
⇒ M = C(µ0H/T)
⇒ M/H = C(µ0/T)
But, M/H = χ, magnetic susceptibility
⇒ χ = C(µ0/T)
Since C and µ0 is constant, magnetic susceptibility is inversely proportional to the absolute temperature i.e.
χ ∝ 1/T
The alignment of the magnetic dipoles in a paramagnetic substance is complete when the applied magnetic field is very large and its temperature is very low.
Applications of Magnetism
[Click Here for Sample Questions]
The following are the applications of magnetism
- There are many applications of magnetism as magnets are used in the majority of products such as electromagnets are used in motors and generators, as well as power supplies.
- Magnetism is used in medical applications such as MRI (magnetic resonance imaging) systems, which are now commonly used in hospitals and medical centers.
- Permanent magnets are created from magnetic materials that are difficult to demagnetize.
- They are used in loudspeakers, headphones, electric meters, and small motors.
- Computers, which are an essential part of modern life, include magnetic mechanisms such as storage devices and magnetic recording in computers.
- A write-head can digitally write in or store data on the dozens of tracks of a floppy disc, which can then be accessed or retrieved by a read-head. In the region where the disk's storage track passes, a write-head generates a strong magnetic field.
Things to Remember
- All materials show magnetic behavior when placed in an external magnetic field.
- Due to the different behavior of materials in magnetic fields they are classified as Diamagnetic, Paramagnetic, and Ferromagnetic materials.
- Diamagnetic materials are weakly magnetized in a direction opposite to the applied magnetic field.
- In diamagnetic materials, electrons in an atom are considered to exist in pairs having orbital motion in opposite directions.
- Paramagnetic materials are weakly magnetized in the direction of the applied magnetic field.
- In paramagnetic materials, electrons of the atoms are considered to have orbital motion as well as spin motion around their axes.
- Ferromagnetic materials are strongly magnetized in the presence of applied magnetic field.
Do check out:
| Chapter Related Links | ||
|---|---|---|
| Magnetic Poles And Their Significance | Curie weiss law | Bar magnet as an equivalent solenoid |
| Current coil | Curie constant | Magnetic levitation project |
Previous Year Questions
- Extraction of metal from the ore cassiterite involves...[JEE Advanced 2011]
- Commonly used vectors for human genome sequencing are...[NEET UG 2014]
- Interfascicular cambium and cork cambium are formed due to..
- Pneumotaxic centre is present in...[UP CPMT 2007]
- Reaction of HBr with propene in the presence of peroxide gives….[NEET UG 2004]
- Assuming the expression for the pressure exerted by the gas on the walls of the container, it can be shown that pressure is...[MHT CET 2016]
- Which among the following is the strongest acid?...[TS EAMCET 2017]
- Isopropyl alcohol on oxidation forms..
- A vector is not changed if..
- Which of the following arrangements does not represent the correct order of the property stated against it?...[JEE Main 2013]
- The major product of the following reaction is...[JEE Main 2019]
- Major product of the following reaction is..[JEE Main 2023]
- The percentage of nitrogen in urea is about..
- The electric field at a point is
- Which of the following statements is true?..[JKCET 2006]
Sample Questions
Ques. What is meant by a magnet? (2 Marks)
Ans. A magnet is a substance or body that generates magnetic fields. These invisible magnetic fields are responsible for magnets' unique property: a force that attracts other ferromagnetic substances such as steel, nickel, iron, cobalt, and so on. They repel or attract other magnets based on the orientation of their poles.
Ques. A salt contains 2 x 1024 molecules each having a dipole moment of 1.5 x 10-23 J/T is kept in a magnetic field of 0.8 T. It is cooled to a temperature of 4 K. It gives saturation of 15%. What is the magnetic moment of the salt for a magnetic field of 1 T and temperature of 3 K? (5 Marks)
Ans. Given
- Number of dipoles, n = 2 x 1024
- Moment of each dipole, m = 1.5 x 10-23 J/T
- Degree of saturation, D = 15%
Effective dipole moment, m1 = 15% of (m x n)
⇒ m1 = (15/100) x 1.5 x 10-23 x 2 x 1024
⇒ m1 = 4.5 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 = 4.5 J T-1
Given
- B1 = 0.8 T
- B2 = 1 T
- T1 = 4 K
- T2 = 3 K
On substituting the values, we get
m2 = 4.5 x (1/0.8) x (4/3) = 7.5 J T-1
Ques. What are the 3 classifications of magnetic materials? (2 Marks)
Ans. Magnetic materials are classified as
- Diamagnetic materials
- Paramagnetic materials
- Ferromagnetic materials
Ques. The phenomenon of perfect diamagnetism is called (2 Marks)
(a) Zero Kelvin Effect
(b) Diamagnetic Effect
(c) Superconductivity
(d) Meissner Effect
Ans. The correct answer is d. Meissner Effect
Explanation: The Meissner effect refers to the phenomena of perfect diamagnetism in superconductors. It's used to magnetically lift high-speed trains.
Ques. Let each iron atom have a dipole moment of 9 x 10-24 A m2. The density of the iron is 8 g/cm3 and the molecular mass is 55 g mol-1. If the domain size of iron is a cube of sides 1 x 10-6 m, find (5 Marks)
(a) Number of atoms in the domain
(b) Maximum dipole moment
(c) Magnetization (M)
Ans. Given
- The dipole moment of each atom, m = 9 x 10-24 A m2
- The density of the iron, ρ = 8 g/cm3 = 8 x 103 kg/m3
- The molecular mass of the iron = 55 g mol-1 = 55 x 10-3 kg mol-1
- Size of each side of the domain cube of iron, a = 1 x 10-6 m
Volume of the domain, V = (a)3
⇒ V = (1 x 10-6)3 = 10-18 m3
Mass of the domain, m’ = ρV
⇒ m’ = (8 x 103) x 10-18 = 8 x 10-15 kg
- Number of atoms in the domain, N = (m’ x Avagadro’s number)/(molecular mass)
⇒ N = (8 x 10-15 x 6.023 x 1023)/(55 x 10-3)
⇒ N = 8.76 x 1010
- Maximum dipole moment, mmax = N x m
⇒ mmax = 8.76 x 1010 x 9 x 10-24 = 7.88 x 10-13 A m2
- Magnetization, M = mmax/V
⇒ M = (7.88 x 10-13)/10-18 = 7.88 x 105 A/m
Ques. Which of the following is a diamagnetic material? (2 Marks)
(a) Calcium
(b) Nitrogen (at STP)
(c) Sodium
(d) Oxygen (at STP)
Ans. The correct answer is b. Nitrogen (at STP)
Explanation: Nitrogen is a diamagnetic material (at STP). Sodium, calcium, and oxygen (at STP) are all paramagnetic.
Ques. Calculate the permeability and susceptibility of a magnetic bar of cross section 0.2 cm2 having a magnetic flux of 3.5 x 10-5 weber due to magnetic intensity of 4500 A m-1. (5 Marks)
Ans. Given
- Area of the cross-section of the magnetic bar, A = 0.2 cm2 = 0.2 x 10-4 m2
- Magnetic intensity, H = 4500 A m-1
- Magnetic flux, Φ = 3.5 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 = (3.5 x 10-5 ) / (0.2 x 10-4 x 4500) = 3.8 x 10-4 T m A-1
Now, magnetic permeability is also given by
µ = µ0(1 + χm)
Where
- µ0 is the absolute permeability
- χm is magnetic susceptibility
⇒ χm = (µ/µ0) - 1
⇒ χm = (3.8 x 10-4 / 4π x 10-7) - 1
⇒ χm = 301.5
Ques. Which of the following is not a constituent of Alnico? (2 Marks)
(a) Magnesium
(b) Iron
(c) Copper
(d) Aluminum
Ans. The correct answer is a. Magnesium
Explanation: Alnico is a kind of hard Ferromagnet. Its magnetization continues even after the field is removed. Its constituent elements are iron, aluminum, cobalt, nickel, and copper.
Ques. Is O2 diamagnetic or paramagnetic? (1 Mark)
Ans. Since O2 contains two unpaired electrons, it is considered to be paramagnetic.
Ques. Define Meissner effect. (2 Marks)
Ans. There is no magnetic field within a superconducting sphere when it is put in a uniform magnetic field. This is known as the Meissner effect. Thus a superconductor is a perfect diamagnetic substance.
Ques. What is the principle behind electromagnets? (2 Marks)
Ans. Electromagnets work on the magnetic effect of an electric current.
It's made of a long coil of insulated copper wire wrapped around a soft iron core that becomes magnetized only when an electric current flows through it.
Ques. What are the different properties of diamagnetic materials? (3 Marks)
Ans. The different properties of diamagnetic materials are
- Diamagnetic materials are always repelled by a magnet.
- Diamagnetic materials are weakly repelled by the magnetic field, therefore in a nonuniform field, these substances move to a weak part of the external magnetic field from a strong part.
- The atomic dipoles in diamagnetic substances are zero since each atom's net magnetic moment is zero due to the existence of paired electrons.
- These materials' magnetic susceptibility is both negative and low. Diamagnetic materials have a slightly lower relative permeability than unity.
- Diamagnetic materials are temperature-independent and do not obey Curie's law.
- Diamagnetic materials have a negative, extremely small intensity that is proportional to the magnetizing field.
Ques. How can you know if something is diamagnetic or paramagnetic? (2 Marks)
Ans. The electron configuration of a substance can be used to determine whether or not it possesses magnetic properties. A material is paramagnetic if its electrons are unpaired; and diamagnetic if all of its electrons are paired.
Ques. What are the different properties of ferromagnetic materials? (3 Marks)
Ans. Ferromagnetic materials exhibit a mechanism known as ferromagnetism. The following are some ferromagnetic material properties:
- When a ferromagnetic rod is put in a magnetic field, it quickly aligns itself in the direction of the magnetic field.
- A ferromagnetic substance has a significant magnetic dipole moment that points in the direction of the magnetizing field.
- In the liquid and gaseous phases, a substance loses its ferromagnetic characteristic.
- A magnet has a strong attraction to ferromagnetic materials.
- Magnetic susceptibility, the intensity of magnetization, and the magnetic flux density of a ferromagnetic material are very large and positive.
Ques. Curie’s law is applicable at every point on a Paramagnetic Material. (2 Marks)
(a) True
(b) False
Ans. The correct answer is b. False
Explanation: As the field or temperature decreases, magnetization increases until it achieves saturation, at the point when all dipoles are completely aligned with the field. Curie's law is no longer applicable beyond this point.
For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates
Check-Out:
Comments