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Class 12 Chapter 5

Class 12 Physics Chapter 5: Magnetism and Matter

Magnetism and Matter is an important chapter in Class 12 Physics that explains the properties of magnets, magnetic materials, and Earth's magnetic field. The chapter covers concepts such as magnetic dipoles, bar magnets, magnetic field lines, magnetization, magnetic susceptibility, magnetic permeability, and the classification of magnetic materials. It also introduces Earth's magnetism and its practical applications. This chapter builds upon the concepts of Moving Charges and Magnetism and is frequently tested in JEE Main and JEE Advanced through conceptual and application-based questions.

At ALLEN, Chapter 5: Magnetism and Matter smart study resources are carefully curated by expert faculty to help students grasp fundamental concepts quickly and revise efficiently before exams. The notes combine concise theory, important formulas, solved examples, previous years' question trends, and exam-focused tips to strengthen conceptual clarity and problem-solving skills. Whether you're preparing for JEE Main, JEE Advanced, or school examinations, these notes provide a structured and effective revision resource to help you score with confidence.

1.0Chapter Snapshot

Parameter	Details
Difficulty Level	Easy to Moderate
JEE Main Weightage	Medium (Generally 1 Question)
JEE Advanced Weightage	Medium (Concept-Based Questions)
Key Concepts Covered	Bar Magnet, Magnetic Dipole, Magnetization, Magnetic Materials, Earth's Magnetism, Magnetic Susceptibility, Permeability

2.0Chapter 1 Smart Study Material by ALLEN Experts: Download PDFs

Continue your preparation by exploring these resources after completing Magnetism and Matter. These study materials will help reinforce concepts, improve problem-solving speed, and strengthen exam readiness.

Practice Resources

Resource	Access
Topic-wise MCQs	Available Soon
Chapter Test	Available Soon
Chapter Mock Test	Available Soon
NCERT Solutions – Chapter 5	Available Soon
JEE Main PYQs with Solutions	Available Soon
JEE Advanced PYQs with Solutions	Available Soon
JEE Important Questions & Solutions on Magnetism and Matter	Available Soon
NEET Important Questions & Solutions on Magnetism and Matter	Available Soon

Must-Revise Concepts

Bar Magnet

Curie constant

Curie weiss law

Diamagnetic ,Paramagnetic ,Ferromagnetic Material

Magnetism and Matter

Magnetism is one of the most fascinating branches of physics, dealing with the interaction of materials with magnetic fields. Matter around us responds differently to a magnetic field depending on its internal structure and alignment of atomic dipoles.

The study of Magnetism and Matter explains:

Why some materials are strongly attracted to magnets,
Why some repel them,
Why Earth itself behaves like a giant magnet.

1.0What is Magnetism?

Magnetism is a fundamental physical phenomenon that arises due to the motion of electric charges. Every electron in an atom has two kinds of motion — orbital motion around the nucleus and spin motion around its own axis. These motions create tiny magnetic dipoles.

When these dipoles cancel each other $\to$ the material shows no net magnetism.
When dipoles align in a particular direction $\to$ the material exhibits magnetism.

Magnetism Examples:

Iron nails stick to a bar magnet because iron is ferromagnetic.
A compass needle aligns itself with Earth’s magnetic field because Earth itself behaves like a giant magnet.

2.0Types of Magnetism

Different materials respond differently when placed in a magnetic field. Based on their behavior, magnetism is classified into three main types:

1. Diamagnetism

Property: Weakly repelled by an external magnetic field.
Cause: Induced magnetic dipoles oppose the applied field.
Susceptibility $(χ)$ : Negative and very small.
Examples: Copper, Bismuth, Silver, Gold, Water.

2. Paramagnetism

Property: Weakly attracted by an external magnetic field.
Cause: Magnetic dipoles tend to align along the applied field but only partially.
Susceptibility $(χ)$ : Small positive value.
Examples: Aluminium, Platinum, Sodium, Lithium.

3. Ferromagnetism

Property: Strongly attracted by a magnetic field and can retain magnetism even after the field is removed.
Cause: Large-scale alignment of magnetic dipoles in the same direction.
Susceptibility $(χ)$ : Very high and positive.
Examples: Iron, Cobalt, Nickel.

3.0Origin of Magnetism in Materials

Atoms consist of electrons revolving around the nucleus.
Each electron has orbital motion and spin motion, both of which contribute to a magnetic moment.
In most atoms, these magnetic effects cancel each other.
In certain materials, alignment of dipoles creates a net magnetic moment, leading to observable magnetism.

Thus, the origin of magnetism lies in the microscopic movement of charges.

1.0Basic Magnetic Quantities and Definitions

Magnetic Dipole

A pair of equal and opposite magnetic poles separated by a small distance.
Example: A bar magnet is a magnetic dipole.

Magnetic Dipole Moment (m)

Defined as the strength of either pole multiplied by the distance between poles.
Vector quantity directed from south pole to north pole of a magnet.

Magnetization (M)

The magnetic moment per unit volume of a material.
Describes how strongly a material is magnetized in an external field.

Magnetic Intensity (H)

The applied magnetic field strength due to an external source (like a solenoid).
Measured in A/m (ampere per meter).

Magnetic Induction (B)

Also called magnetic flux density.
Describes the actual magnetic field inside a material.
Related to $(B = μ_{0} (H + M))$ .

2.0Magnetic Properties of Materials

Diamagnetic Materials

Very weakly repelled by a magnetic field.
Do not retain magnetism after the field is removed.
Magnetic susceptibility $((χ))$ is negative.
Examples: Copper, Silver, Gold, Water.

Paramagnetic Materials

Weakly attracted by a magnetic field.
The effect disappears when the field is removed.
Magnetic susceptibility is small and positive.
Examples: Aluminium, Platinum, Sodium.

Ferromagnetic Materials

Strongly attracted by a magnetic field.
Can retain magnetism even after the field is removed (permanent magnets).
Large and positive susceptibility.
Examples: Iron, Cobalt, Nickel.

3.0Magnetic Susceptibility and Permeability

Magnetic Susceptibility $(x_{m})$

$χ_{m} = \frac{I}{H}$ [It is a scalar with no units & dimensions]

Physically it represents the ease with which a magnetic material can be magnetised.

Note:- A material with more $χ_{m}$ , can be change into magnet easily.

Magnetic Permeability $(μ)$

$μ = \frac{B}{H} = \frac{Total magnetic field inside a material}{Magnetizing field}$

Unit of $μ = μ = \frac{B _{m}}{H} = \frac{Wb / m ^{2}}{A / m} = \frac{Weber}{A - m} = \frac{H - A}{A - m} = \frac{H}{m}$

It represents the degree up to which a material can be penetrated by the magnetic field lines.

Relative Permeability $(μ_{r})$

$μ_{r} = \frac{μ}{μ _{0}}$

It has no units and dimensions

Relation between $μ$ and $χ_{m}$

When a magnetic material is placed in a magnetic field $B_{0}$ for magnetization, then total magnetic field in the material is

$B_{m} = B_{0} + B_{in} {B_{in} = induced field}$

$∵ B_{0} = μ_{0} H; B_{in} = μ_{0} I$

$∵ B_{m} = μ_{0} (H + I)$

$B_{m} = μ_{0} (H + I)$

$μ H = μ_{0} H (1 + \frac{I}{H})$

$μ = μ_{0} (1 + χ_{m})$

$\frac{μ}{μ _{0}} = (1 + χ_{m})$

$μ_{r} = (1 + χ_{m})$

For vacuum, $μ_{r} = 1, χ_{m} = 0$

For air, $μ_{r} = 1.04, χ_{m} = 0.04$

4.0Hysteresis in Magnetic Materials

When a ferromagnetic material is repeatedly magnetized and demagnetized:

The magnetization does not follow the same path during increase and decrease of field.
The graph of ( B ) vs ( H ) shows a hysteresis loop.
Key points:
- Retentivity: Ability to retain magnetism.
- Coercivity: Field required to demagnetize completely.
Soft iron: low coercivity (used in transformers).
Steel: high coercivity (used in permanent magnets).

5.0Earth’s Magnetism

Earth behaves like a huge bar magnet tilted slightly with respect to its rotation axis.

Magnetic Elements of Earth

Magnetic Declination (D): Angle between geographic meridian and magnetic meridian.

Magnetic Inclination (Dip): Angle between Earth’s magnetic field and the horizontal plane.

Horizontal Component (H): Component of Earth’s field along the horizontal plane.

Relation:

$B^{2} = H^{2} + Z^{2}$

where $(B) =$ total intensity, $(Z) =$ vertical component.

6.0Bar Magnet as an Equivalent Solenoid

A bar magnet produces a magnetic field similar to that of a solenoid.
Magnetic moment of a solenoid:
$[M = nI A]$ where ( n ) = turns per unit length, ( I ) = current, ( A ) = cross-sectional area.

This helps in theoretical treatment of bar magnets using solenoid concepts.

7.0Torque on a Magnetic Dipole in a Uniform Magnetic Field

Torque and Force on Magnetic Dipole

Torque on a Magnetic Dipole in Uniform Magnetic Field

When a bar magnet is placed in a uniform magnetic field the two poles experience a force. They are equal in magnitude and opposite in direction and do not have same line of action. They constitute a couple of forces which produces a torque. The torque tries to rotate the magnet so as to align it parallel too direction of field

Torque due to force couple

Bar Magnet

Consider a bar magnet of magnetic moment $M$ held in a uniform magnetic field $B$ making an angle $θ$ with the field,then the magnet experiences a torque given by,

$τ = force \times perpendicular distance between force couple$

$τ = F (l sin θ)$

$τ = (m B) (l sin θ)$

$τ = m l (B sin θ)$

$τ = MB sin θ, where M = m l$

$τ = M \times B$

$τ = MB sin θ$

Case-1:If $θ = 9 0^{\circ} \Rightarrow τ = MB (maximum)$

Case-2:If $θ = 0^{\circ} or 18 0^{\circ} \Rightarrow τ = 0 (minimum)$

Coil or Loop: If a loop carries a current of magnitude I and magnetic moment $M$ held in a uniform magnetic field $B$ making an angle \theta Then the loop experiences a torque given by

$τ = M \times B$

$τ = MB sin θ$

$τ = I (A \times B)$

If loop have N turns then

$τ = N I (A \times B)$

$τ = N I A B sin θ$

Case-1:If $θ = 9 0^{\circ} \Rightarrow τ = N I A B (maximum)$

Case-2:If $θ = 0^{\circ} or 18 0^{\circ} \Rightarrow τ = 0 (minimum)$

Illustration-1. A magnetic Moment $50 \hat{i} A - m^{2}$ placed along x-axis. When magnetic field is $B = (0.5 \hat{i} + 0.3 \hat{j}) Tesla$ .The torque acting on magnet is:-

Solution:

$τ = M \times B$

$\hat{i} 50 0.5 \hat{j} 03 \hat{k} 00 =$

$(0) \hat{i} - (0) \hat{j} + (150) \hat{k} N - m = 150 \hat{k} N - m$

Illustration-2: A uniform magnetic field of 5000 gauss is established along the positive z-direction. A rectangular loop of side 20 cm and 5 cm carries a current of 10 A is suspended in this magnetic field. What is the torque on the loop in the different cases shown in the following figures? What is the force in each case? Which case corresponds to stable equilibrium?

Solution:

1. Torque on loop, $τ = B I A sin θ$

Here $θ = 9 0^{\circ}, B = 5000 Gauss = 5000 \times 1 0^{- 4} = 0.5 Tesla$

$I = 10 Ampere, A = 20 \times 5 cm^{2} = 100 \times 1 0^{- 4} = 1 0^{- 2} m^{2}$

Now $τ = 0.5 \times 10 \times 1 0^{- 2} = 5 \times 1 0^{- 2} N - m . I t i s d i rec t e d a l o n g - Ya x i s$

2. Same as $(a)$

3. $τ = 5 \times 1 0^{- 2} N - ma l o n gx - d i rec t i o n$

4. $τ = 5 \times 1 0^{- 2} N - ma t anan g l eo f 24 0^{\circ} w i t h + x d i rec t i o n .$

5. $τ$ is zero[∵ Angle between plane of loop and direction of magnetic field is $9 0^{\circ}$ ]

Resultant force is zero in each case. Case (e) corresponds to stable equilibrium.

Illustration-3:A solenoid of 200 turns/m is carrying a current of 5A. Relative permeability of core material of solenoid is 3000. Determine the magnitudes of the magnetic intensity, magnetization and the magnetic field inside the core.

Solution:

Magnetic Intensity $H = ni = 200 m^{- 1} \times 5 A = 1000 Am^{- 1}$

$μ_{r} = 1 + χ i.e χ = 3000 - 1 = 2999$

Hence the magnetization $I = χH = 2.999 \times 1 0^{6} Am^{- 1}$

The magnetic field $B = μ_{0} μ_{r} H = 3000 μ_{0} H = 3000 \times 4 π \times 1 0^{- 7} \times 1000 = 3.769 T$

Illustration-4: A rod of magnetic material of cross section $0.25 cm^{2}$ is located in $4000 A / m$ magnetising field. Magnetic flux passes through the rod is $25 \times 1 0^{- 6} Wb$ . Find out for rod

(i) permeability

(ii) magnetic susceptibility

(iii) magnetisation

Solution:

(i) Magnetic Flux $ϕ = B A \Rightarrow B = \frac{ϕ}{A} = \frac{25 \times 1 0 ^{- 6}}{0.25 \times 1 0 ^{- 4}} = 1 Wb / m^{2}$

(ii) $μ_{r} = 1 + χ_{m} χ_{m} = μ_{r} - 1 (∵ μ_{r} = \frac{μ}{μ _{0}})$

$χ_{m} = \frac{μ}{μ _{0}} - 1 = (\frac{2.5 \times 1 0 ^{- 4}}{4 π \times 1 0 ^{- 7}} - 1) = 199 - 1 = 198$

(iii) magnetisation $I = χ_{m} H = 198 \times 4000 = 7.92 \times 1 0^{5} A / m$

8.0Applications of Magnetism and Matter in Real Life

Electromagnets used in cranes for lifting heavy loads.
Transformers and generators use soft iron cores.
Permanent magnets made of steel are used in electric meters, compasses, loudspeakers.
Earth’s magnetic field helps in navigation using a magnetic compass.
Data storage in hard disks uses magnetic domains.

1.0Learning Outcomes

After completing these Magnetism and Matter Revision Notes, you will be able to:

Understand the concept of magnetic dipoles and bar magnets.
Explain magnetic field lines and magnetic field intensity.
Differentiate between diamagnetic, paramagnetic, and ferromagnetic materials.
Understand magnetic susceptibility, permeability, and magnetization.
Analyze the magnetic properties of various substances.
Explain Earth's magnetic field and its important elements.
Apply concepts of magnetic materials to solve conceptual and numerical questions.
Strengthen problem-solving skills by mastering concepts frequently tested in JEE Main and JEE Advanced.

2.05-Minute Quick Revision

If you have only 5 minutes before your exam or mock test, focus on revising these high-weightage concepts and formulas to maximize your score.

Must-Revise Concepts

Magnetic Dipole
Bar Magnet
Magnetic Field Lines
Magnetization
Magnetic Susceptibility
Magnetic Permeability
Diamagnetic Materials
Paramagnetic Materials
Ferromagnetic Materials
Earth's Magnetism

Important Formula Recall

Before attempting numerical questions, quickly revise these essential formulas:

Magnetic Dipole Moment
Torque on Magnetic Dipole
Magnetic Field due to Bar Magnet
Relation between Magnetization and Magnetic Field
Magnetic Susceptibility
Magnetic Permeability
Horizontal Component of Earth's Magnetic Field
Magnetic Inclination and Declination

3.0High Weightage Topics

The following topics have consistently appeared in JEE Main and JEE Advanced examinations and should be given higher priority during revision.

Topic	Focus Area
Bar Magnet	Magnetic dipole properties
Magnetic Dipole Moment	Torque and potential energy
Magnetic Materials	Diamagnetic, paramagnetic, ferromagnetic
Magnetization	Magnetic domains and intensity
Magnetic Susceptibility	Material response to magnetic field
Earth's Magnetism	Inclination, declination, magnetic elements
Magnetic Permeability	Relation with magnetic field
Hysteresis Curve	Magnetic memory and applications

4.0Formula Handbook

The following formulas are the most important for solving JEE Main and JEE Advanced questions from Magnetism and Matter.

(Formula section continues here.)

5.0Common Mistakes & JEE Tips

Magnetism and Matter is a concept-oriented chapter where students often lose marks due to confusion between different magnetic quantities and magnetic materials. Avoiding these mistakes can significantly improve your performance in JEE Main and JEE Advanced.

Common Mistake	Correct Approach
Confusing magnetic field with magnetic field intensity	Understand the difference between B and H and their units.
Mixing magnetic susceptibility and permeability	Susceptibility measures response to a magnetic field, while permeability indicates ease of magnetization.
Confusing diamagnetic, paramagnetic, and ferromagnetic materials	Learn the distinguishing properties and examples of each type.
Using incorrect direction of magnetic field lines	Magnetic field lines emerge from the north pole and enter the south pole outside the magnet.
Ignoring Earth's magnetic elements	Revise inclination, declination, and horizontal component carefully.
Incorrect magnetic dipole moment formula	Memorize the correct expression and SI unit.
Confusing torque and potential energy formulas	Apply the correct equation depending on the given conditions.
Incorrect SI unit conversion	Always use Tesla (T), Weber (Wb), Ampere (A), and A·m² where applicable.

6.0ALLEN Faculty Tips

Memorize the characteristics of diamagnetic, paramagnetic, and ferromagnetic materials using comparison tables.
Practice conceptual questions on Earth's magnetism regularly.
Draw neat diagrams for magnetic field lines and magnetic domains.
Revise the relationships among magnetic field, magnetization, susceptibility, and permeability.
Focus on conceptual PYQs, as this chapter is largely theory-based.
Revise formulas for magnetic dipole moment and torque before the exam.

7.0PYQ Trend Analysis

Magnetism and Matter is a medium-weightage chapter in Class 12 Physics for both JEE Main and JEE Advanced. Questions are primarily conceptual, with occasional numerical problems involving magnetic dipoles, Earth's magnetism, and magnetic materials.

Note: The trend below is based on the analysis of previous years' JEE Main and JEE Advanced question papers. The exact number of questions may vary each year.

Concept	Questions Asked (Last 5 Years)	Average Difficulty
Magnetic Dipole	3–4	Easy
Magnetic Materials	4–5	Easy–Moderate
Magnetization & Susceptibility	3–4	Moderate
Earth's Magnetism	3–4	Moderate
Magnetic Permeability	2–3	Easy
Hysteresis	1–2	Moderate

Most Common Question Types

Properties of bar magnets and magnetic dipoles.
Classification of magnetic materials.
Magnetic susceptibility and permeability.
Earth's magnetic field and magnetic elements.
Torque on magnetic dipoles.
Assertion–Reason and conceptual MCQs.

8.0Smart Revision Strategy

If you're short on time, revise the chapter in the following order:

Magnetic Dipole & Bar Magnet
Magnetic Field Lines
Diamagnetic, Paramagnetic & Ferromagnetic Materials
Magnetization
Magnetic Susceptibility
Magnetic Permeability
Earth's Magnetism
Hysteresis Curve
PYQs and Important Concept-Based Questions

Class 12 Physics Chapters List:- JEE & NEET Revision Notes

Chapter 1 Electric Charges and Fields

Chapter 2 Electrostatic Potential and Capacitance

Chapter 3 Current Electricity

Chapter 4 Moving Charges and Magnetism

Chapter 5 Magnetism and Matter

Chapter 6 Electromagnetic Induction

Chapter 7 Alternating Current

Chapter 8 Electromagnetic Waves

Chapter 9 Ray Optics and Optical Instruments

Chapter 10 Wave Optics

Chapter 11 Dual Nature of Radiation and Matter

Chapter 12 Atoms

Chapter 13 Nuclei

Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits

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Class 12 Physics Chapter 5: Magnetism and Matter

Magnetism and Matter is an important chapter in Class 12 Physics that explains the properties of magnets, magnetic materials, and Earth's magnetic field. The chapter covers concepts such as magnetic dipoles, bar magnets, magnetic field lines, magnetization, magnetic susceptibility, magnetic permeability, and the classification of magnetic materials. It also introduces Earth's magnetism and its practical applications. This chapter builds upon the concepts of Moving Charges and Magnetism and is frequently tested in JEE Main and JEE Advanced through conceptual and application-based questions.

At ALLEN, Chapter 5: Magnetism and Matter smart study resources are carefully curated by expert faculty to help students grasp fundamental concepts quickly and revise efficiently before exams. The notes combine concise theory, important formulas, solved examples, previous years' question trends, and exam-focused tips to strengthen conceptual clarity and problem-solving skills. Whether you're preparing for JEE Main, JEE Advanced, or school examinations, these notes provide a structured and effective revision resource to help you score with confidence.

1.0Chapter Snapshot

Parameter	Details
Difficulty Level	Easy to Moderate
JEE Main Weightage	Medium (Generally 1 Question)
JEE Advanced Weightage	Medium (Concept-Based Questions)
Key Concepts Covered	Bar Magnet, Magnetic Dipole, Magnetization, Magnetic Materials, Earth's Magnetism, Magnetic Susceptibility, Permeability

2.0Chapter 1 Smart Study Material by ALLEN Experts: Download PDFs

Continue your preparation by exploring these resources after completing Magnetism and Matter. These study materials will help reinforce concepts, improve problem-solving speed, and strengthen exam readiness.

Practice Resources

Resource	Access
Topic-wise MCQs	Available Soon
Chapter Test	Available Soon
Chapter Mock Test	Available Soon
NCERT Solutions – Chapter 5	Available Soon
JEE Main PYQs with Solutions	Available Soon
JEE Advanced PYQs with Solutions	Available Soon
JEE Important Questions & Solutions on Magnetism and Matter	Available Soon
NEET Important Questions & Solutions on Magnetism and Matter	Available Soon

Magnetism and Matter

Magnetism is one of the most fascinating branches of physics, dealing with the interaction of materials with magnetic fields. Matter around us responds differently to a magnetic field depending on its internal structure and alignment of atomic dipoles.

The study of Magnetism and Matter explains:

Why some materials are strongly attracted to magnets,
Why some repel them,
Why Earth itself behaves like a giant magnet.

1.0What is Magnetism?

Magnetism is a fundamental physical phenomenon that arises due to the motion of electric charges. Every electron in an atom has two kinds of motion — orbital motion around the nucleus and spin motion around its own axis. These motions create tiny magnetic dipoles.

When these dipoles cancel each other $\to$ the material shows no net magnetism.
When dipoles align in a particular direction $\to$ the material exhibits magnetism.

Magnetism Examples:

Iron nails stick to a bar magnet because iron is ferromagnetic.
A compass needle aligns itself with Earth’s magnetic field because Earth itself behaves like a giant magnet.

2.0Types of Magnetism

Different materials respond differently when placed in a magnetic field. Based on their behavior, magnetism is classified into three main types:

1. Diamagnetism

Property: Weakly repelled by an external magnetic field.
Cause: Induced magnetic dipoles oppose the applied field.
Susceptibility $(χ)$ : Negative and very small.
Examples: Copper, Bismuth, Silver, Gold, Water.

2. Paramagnetism

Property: Weakly attracted by an external magnetic field.
Cause: Magnetic dipoles tend to align along the applied field but only partially.
Susceptibility $(χ)$ : Small positive value.
Examples: Aluminium, Platinum, Sodium, Lithium.

3. Ferromagnetism

Property: Strongly attracted by a magnetic field and can retain magnetism even after the field is removed.
Cause: Large-scale alignment of magnetic dipoles in the same direction.
Susceptibility $(χ)$ : Very high and positive.
Examples: Iron, Cobalt, Nickel.

3.0Origin of Magnetism in Materials

Atoms consist of electrons revolving around the nucleus.
Each electron has orbital motion and spin motion, both of which contribute to a magnetic moment.
In most atoms, these magnetic effects cancel each other.
In certain materials, alignment of dipoles creates a net magnetic moment, leading to observable magnetism.

Thus, the origin of magnetism lies in the microscopic movement of charges.

1.0Basic Magnetic Quantities and Definitions

Magnetic Dipole

A pair of equal and opposite magnetic poles separated by a small distance.
Example: A bar magnet is a magnetic dipole.

Magnetic Dipole Moment (m)

Defined as the strength of either pole multiplied by the distance between poles.
Vector quantity directed from south pole to north pole of a magnet.

Magnetization (M)

The magnetic moment per unit volume of a material.
Describes how strongly a material is magnetized in an external field.

Magnetic Intensity (H)

The applied magnetic field strength due to an external source (like a solenoid).
Measured in A/m (ampere per meter).

Magnetic Induction (B)

Also called magnetic flux density.
Describes the actual magnetic field inside a material.
Related to $(B = μ_{0} (H + M))$ .

2.0Magnetic Properties of Materials

Diamagnetic Materials

Very weakly repelled by a magnetic field.
Do not retain magnetism after the field is removed.
Magnetic susceptibility $((χ))$ is negative.
Examples: Copper, Silver, Gold, Water.

Paramagnetic Materials

Weakly attracted by a magnetic field.
The effect disappears when the field is removed.
Magnetic susceptibility is small and positive.
Examples: Aluminium, Platinum, Sodium.

Ferromagnetic Materials

Strongly attracted by a magnetic field.
Can retain magnetism even after the field is removed (permanent magnets).
Large and positive susceptibility.
Examples: Iron, Cobalt, Nickel.

3.0Magnetic Susceptibility and Permeability

Magnetic Susceptibility $(x_{m})$

$χ_{m} = \frac{I}{H}$ [It is a scalar with no units & dimensions]

Physically it represents the ease with which a magnetic material can be magnetised.

Note:- A material with more $χ_{m}$ , can be change into magnet easily.

Magnetic Permeability $(μ)$

$μ = \frac{B}{H} = \frac{Total magnetic field inside a material}{Magnetizing field}$

Unit of $μ = μ = \frac{B _{m}}{H} = \frac{Wb / m ^{2}}{A / m} = \frac{Weber}{A - m} = \frac{H - A}{A - m} = \frac{H}{m}$

It represents the degree up to which a material can be penetrated by the magnetic field lines.

Relative Permeability $(μ_{r})$

$μ_{r} = \frac{μ}{μ _{0}}$

It has no units and dimensions

Relation between $μ$ and $χ_{m}$

When a magnetic material is placed in a magnetic field $B_{0}$ for magnetization, then total magnetic field in the material is

$B_{m} = B_{0} + B_{in} {B_{in} = induced field}$

$∵ B_{0} = μ_{0} H; B_{in} = μ_{0} I$

$∵ B_{m} = μ_{0} (H + I)$

$B_{m} = μ_{0} (H + I)$

$μ H = μ_{0} H (1 + \frac{I}{H})$

$μ = μ_{0} (1 + χ_{m})$

$\frac{μ}{μ _{0}} = (1 + χ_{m})$

$μ_{r} = (1 + χ_{m})$

For vacuum, $μ_{r} = 1, χ_{m} = 0$

For air, $μ_{r} = 1.04, χ_{m} = 0.04$

4.0Hysteresis in Magnetic Materials

When a ferromagnetic material is repeatedly magnetized and demagnetized:

The magnetization does not follow the same path during increase and decrease of field.
The graph of ( B ) vs ( H ) shows a hysteresis loop.
Key points:
- Retentivity: Ability to retain magnetism.
- Coercivity: Field required to demagnetize completely.
Soft iron: low coercivity (used in transformers).
Steel: high coercivity (used in permanent magnets).

5.0Earth’s Magnetism

Earth behaves like a huge bar magnet tilted slightly with respect to its rotation axis.

Magnetic Elements of Earth

Magnetic Declination (D): Angle between geographic meridian and magnetic meridian.

Magnetic Inclination (Dip): Angle between Earth’s magnetic field and the horizontal plane.

Horizontal Component (H): Component of Earth’s field along the horizontal plane.

Relation:

$B^{2} = H^{2} + Z^{2}$

where $(B) =$ total intensity, $(Z) =$ vertical component.

6.0Bar Magnet as an Equivalent Solenoid

A bar magnet produces a magnetic field similar to that of a solenoid.
Magnetic moment of a solenoid:
$[M = nI A]$ where ( n ) = turns per unit length, ( I ) = current, ( A ) = cross-sectional area.

This helps in theoretical treatment of bar magnets using solenoid concepts.

7.0Torque on a Magnetic Dipole in a Uniform Magnetic Field

Torque and Force on Magnetic Dipole

Torque on a Magnetic Dipole in Uniform Magnetic Field

When a bar magnet is placed in a uniform magnetic field the two poles experience a force. They are equal in magnitude and opposite in direction and do not have same line of action. They constitute a couple of forces which produces a torque. The torque tries to rotate the magnet so as to align it parallel too direction of field

Torque due to force couple

Bar Magnet

Consider a bar magnet of magnetic moment $M$ held in a uniform magnetic field $B$ making an angle $θ$ with the field,then the magnet experiences a torque given by,

$τ = force \times perpendicular distance between force couple$

$τ = F (l sin θ)$

$τ = (m B) (l sin θ)$

$τ = m l (B sin θ)$

$τ = MB sin θ, where M = m l$

$τ = M \times B$

$τ = MB sin θ$

Case-1:If $θ = 9 0^{\circ} \Rightarrow τ = MB (maximum)$

Case-2:If $θ = 0^{\circ} or 18 0^{\circ} \Rightarrow τ = 0 (minimum)$

Coil or Loop: If a loop carries a current of magnitude I and magnetic moment $M$ held in a uniform magnetic field $B$ making an angle \theta Then the loop experiences a torque given by

$τ = M \times B$

$τ = MB sin θ$

$τ = I (A \times B)$

If loop have N turns then

$τ = N I (A \times B)$

$τ = N I A B sin θ$

Case-1:If $θ = 9 0^{\circ} \Rightarrow τ = N I A B (maximum)$

Case-2:If $θ = 0^{\circ} or 18 0^{\circ} \Rightarrow τ = 0 (minimum)$

Illustration-1. A magnetic Moment $50 \hat{i} A - m^{2}$ placed along x-axis. When magnetic field is $B = (0.5 \hat{i} + 0.3 \hat{j}) Tesla$ .The torque acting on magnet is:-

Solution:

$τ = M \times B$

$\hat{i} 50 0.5 \hat{j} 03 \hat{k} 00 =$

$(0) \hat{i} - (0) \hat{j} + (150) \hat{k} N - m = 150 \hat{k} N - m$

Illustration-2: A uniform magnetic field of 5000 gauss is established along the positive z-direction. A rectangular loop of side 20 cm and 5 cm carries a current of 10 A is suspended in this magnetic field. What is the torque on the loop in the different cases shown in the following figures? What is the force in each case? Which case corresponds to stable equilibrium?

Solution:

1. Torque on loop, $τ = B I A sin θ$

Here $θ = 9 0^{\circ}, B = 5000 Gauss = 5000 \times 1 0^{- 4} = 0.5 Tesla$

$I = 10 Ampere, A = 20 \times 5 cm^{2} = 100 \times 1 0^{- 4} = 1 0^{- 2} m^{2}$

Now $τ = 0.5 \times 10 \times 1 0^{- 2} = 5 \times 1 0^{- 2} N - m . I t i s d i rec t e d a l o n g - Ya x i s$

2. Same as $(a)$

3. $τ = 5 \times 1 0^{- 2} N - ma l o n gx - d i rec t i o n$

4. $τ = 5 \times 1 0^{- 2} N - ma t anan g l eo f 24 0^{\circ} w i t h + x d i rec t i o n .$

5. $τ$ is zero[∵ Angle between plane of loop and direction of magnetic field is $9 0^{\circ}$ ]

Resultant force is zero in each case. Case (e) corresponds to stable equilibrium.

Illustration-3:A solenoid of 200 turns/m is carrying a current of 5A. Relative permeability of core material of solenoid is 3000. Determine the magnitudes of the magnetic intensity, magnetization and the magnetic field inside the core.

Solution:

Magnetic Intensity $H = ni = 200 m^{- 1} \times 5 A = 1000 Am^{- 1}$

$μ_{r} = 1 + χ i.e χ = 3000 - 1 = 2999$

Hence the magnetization $I = χH = 2.999 \times 1 0^{6} Am^{- 1}$

The magnetic field $B = μ_{0} μ_{r} H = 3000 μ_{0} H = 3000 \times 4 π \times 1 0^{- 7} \times 1000 = 3.769 T$

Illustration-4: A rod of magnetic material of cross section $0.25 cm^{2}$ is located in $4000 A / m$ magnetising field. Magnetic flux passes through the rod is $25 \times 1 0^{- 6} Wb$ . Find out for rod

(i) permeability

(ii) magnetic susceptibility

(iii) magnetisation

Solution:

(i) Magnetic Flux $ϕ = B A \Rightarrow B = \frac{ϕ}{A} = \frac{25 \times 1 0 ^{- 6}}{0.25 \times 1 0 ^{- 4}} = 1 Wb / m^{2}$

(ii) $μ_{r} = 1 + χ_{m} χ_{m} = μ_{r} - 1 (∵ μ_{r} = \frac{μ}{μ _{0}})$

$χ_{m} = \frac{μ}{μ _{0}} - 1 = (\frac{2.5 \times 1 0 ^{- 4}}{4 π \times 1 0 ^{- 7}} - 1) = 199 - 1 = 198$

(iii) magnetisation $I = χ_{m} H = 198 \times 4000 = 7.92 \times 1 0^{5} A / m$

8.0Applications of Magnetism and Matter in Real Life

Electromagnets used in cranes for lifting heavy loads.
Transformers and generators use soft iron cores.
Permanent magnets made of steel are used in electric meters, compasses, loudspeakers.
Earth’s magnetic field helps in navigation using a magnetic compass.
Data storage in hard disks uses magnetic domains.

1.0Learning Outcomes

After completing these Magnetism and Matter Revision Notes, you will be able to:

Understand the concept of magnetic dipoles and bar magnets.
Explain magnetic field lines and magnetic field intensity.
Differentiate between diamagnetic, paramagnetic, and ferromagnetic materials.
Understand magnetic susceptibility, permeability, and magnetization.
Analyze the magnetic properties of various substances.
Explain Earth's magnetic field and its important elements.
Apply concepts of magnetic materials to solve conceptual and numerical questions.
Strengthen problem-solving skills by mastering concepts frequently tested in JEE Main and JEE Advanced.

2.05-Minute Quick Revision

If you have only 5 minutes before your exam or mock test, focus on revising these high-weightage concepts and formulas to maximize your score.

Must-Revise Concepts

Magnetic Dipole
Bar Magnet
Magnetic Field Lines
Magnetization
Magnetic Susceptibility
Magnetic Permeability
Diamagnetic Materials
Paramagnetic Materials
Ferromagnetic Materials
Earth's Magnetism

Important Formula Recall

Before attempting numerical questions, quickly revise these essential formulas:

Magnetic Dipole Moment
Torque on Magnetic Dipole
Magnetic Field due to Bar Magnet
Relation between Magnetization and Magnetic Field
Magnetic Susceptibility
Magnetic Permeability
Horizontal Component of Earth's Magnetic Field
Magnetic Inclination and Declination

3.0High Weightage Topics

The following topics have consistently appeared in JEE Main and JEE Advanced examinations and should be given higher priority during revision.

Topic	Focus Area
Bar Magnet	Magnetic dipole properties
Magnetic Dipole Moment	Torque and potential energy
Magnetic Materials	Diamagnetic, paramagnetic, ferromagnetic
Magnetization	Magnetic domains and intensity
Magnetic Susceptibility	Material response to magnetic field
Earth's Magnetism	Inclination, declination, magnetic elements
Magnetic Permeability	Relation with magnetic field
Hysteresis Curve	Magnetic memory and applications

4.0Formula Handbook

The following formulas are the most important for solving JEE Main and JEE Advanced questions from Magnetism and Matter.

(Formula section continues here.)

5.0Common Mistakes & JEE Tips

Magnetism and Matter is a concept-oriented chapter where students often lose marks due to confusion between different magnetic quantities and magnetic materials. Avoiding these mistakes can significantly improve your performance in JEE Main and JEE Advanced.

Common Mistake	Correct Approach
Confusing magnetic field with magnetic field intensity	Understand the difference between B and H and their units.
Mixing magnetic susceptibility and permeability	Susceptibility measures response to a magnetic field, while permeability indicates ease of magnetization.
Confusing diamagnetic, paramagnetic, and ferromagnetic materials	Learn the distinguishing properties and examples of each type.
Using incorrect direction of magnetic field lines	Magnetic field lines emerge from the north pole and enter the south pole outside the magnet.
Ignoring Earth's magnetic elements	Revise inclination, declination, and horizontal component carefully.
Incorrect magnetic dipole moment formula	Memorize the correct expression and SI unit.
Confusing torque and potential energy formulas	Apply the correct equation depending on the given conditions.
Incorrect SI unit conversion	Always use Tesla (T), Weber (Wb), Ampere (A), and A·m² where applicable.

6.0ALLEN Faculty Tips

Memorize the characteristics of diamagnetic, paramagnetic, and ferromagnetic materials using comparison tables.
Practice conceptual questions on Earth's magnetism regularly.
Draw neat diagrams for magnetic field lines and magnetic domains.
Revise the relationships among magnetic field, magnetization, susceptibility, and permeability.
Focus on conceptual PYQs, as this chapter is largely theory-based.
Revise formulas for magnetic dipole moment and torque before the exam.

7.0PYQ Trend Analysis

Magnetism and Matter is a medium-weightage chapter in Class 12 Physics for both JEE Main and JEE Advanced. Questions are primarily conceptual, with occasional numerical problems involving magnetic dipoles, Earth's magnetism, and magnetic materials.

Note: The trend below is based on the analysis of previous years' JEE Main and JEE Advanced question papers. The exact number of questions may vary each year.

Concept	Questions Asked (Last 5 Years)	Average Difficulty
Magnetic Dipole	3–4	Easy
Magnetic Materials	4–5	Easy–Moderate
Magnetization & Susceptibility	3–4	Moderate
Earth's Magnetism	3–4	Moderate
Magnetic Permeability	2–3	Easy
Hysteresis	1–2	Moderate

Most Common Question Types

Properties of bar magnets and magnetic dipoles.
Classification of magnetic materials.
Magnetic susceptibility and permeability.
Earth's magnetic field and magnetic elements.
Torque on magnetic dipoles.
Assertion–Reason and conceptual MCQs.

8.0Smart Revision Strategy

If you're short on time, revise the chapter in the following order:

Magnetic Dipole & Bar Magnet
Magnetic Field Lines
Diamagnetic, Paramagnetic & Ferromagnetic Materials
Magnetization
Magnetic Susceptibility
Magnetic Permeability
Earth's Magnetism
Hysteresis Curve
PYQs and Important Concept-Based Questions

Frequently Asked Questions

What is Magnetism and Matter in Class 12 Physics?

Which topics are important in Magnetism and Matter?

Why is the hysteresis curve important in Magnetism and Matter?

How are magnetic materials classified?

Is Magnetism and Matter important for JEE Main and NEET?

Join ALLEN!

Class 12 Physics Chapter 5: Magnetism and Matter

1.0Chapter Snapshot

2.0Chapter 1 Smart Study Material by ALLEN Experts: Download PDFs

Practice Resources

On this page

Magnetism and Matter

1.0What is Magnetism?

2.0Types of Magnetism

1. Diamagnetism

2. Paramagnetism

3. Ferromagnetism

3.0Origin of Magnetism in Materials

On this page

1.0Learning Outcomes

2.05-Minute Quick Revision

Must-Revise Concepts

Important Formula Recall

3.0High Weightage Topics

4.0Formula Handbook

5.0Common Mistakes & JEE Tips

6.0ALLEN Faculty Tips

7.0PYQ Trend Analysis

Most Common Question Types

8.0Smart Revision Strategy

On this page

Frequently Asked Questions

What is Magnetism and Matter in Class 12 Physics?

Which topics are important in Magnetism and Matter?

Why is the hysteresis curve important in Magnetism and Matter?

How are magnetic materials classified?

Is Magnetism and Matter important for JEE Main and NEET?

Join ALLEN!

Class 12 Physics Chapter 5: Magnetism and Matter

1.0Chapter Snapshot

2.0Chapter 1 Smart Study Material by ALLEN Experts: Download PDFs

Practice Resources

On this page

Magnetism and Matter

1.0What is Magnetism?

2.0Types of Magnetism

1. Diamagnetism

2. Paramagnetism

3. Ferromagnetism

3.0Origin of Magnetism in Materials

On this page

1.0Learning Outcomes

2.05-Minute Quick Revision

Must-Revise Concepts

Important Formula Recall

3.0High Weightage Topics

4.0Formula Handbook

5.0Common Mistakes & JEE Tips

6.0ALLEN Faculty Tips

7.0PYQ Trend Analysis

Most Common Question Types

8.0Smart Revision Strategy

On this page