Magnetism and Matter Class 12 Physics Notes 2026-27 | Chapter 5
Official CBSE Physics Curriculum 2026–27 · Official Class XII 2026–27 SQP & Marking Scheme
1. What You Will Learn in Chapter 5
Chapter 4 showed how electric currents and moving charges are connected with magnetic fields. Chapter 5 shifts the focus to magnets themselves and the behaviour of matter in magnetic fields.
A bar magnet behaves as a magnetic dipole with two inseparable poles.
The field pattern of a bar magnet can be understood qualitatively through the equivalent-solenoid picture.
A magnetic dipole placed in a uniform magnetic field can experience a torque that tends to align it with the field.
Materials respond differently to an applied magnetic field and are classified as diamagnetic, paramagnetic or ferromagnetic.
2. Bar Magnet and Magnetic Dipole
A bar magnet has two poles, conventionally called north (N) and south (S). The poles occur in pairs. If a bar magnet is cut into smaller pieces, the pieces do not produce isolated magnetic poles; each piece behaves as a smaller magnet with both north and south poles.
Basic properties of a bar magnet
- Like magnetic poles repel and unlike magnetic poles attract.
- A freely suspended bar magnet tends to align approximately along the north–south direction.
- Magnetic field lines provide a visual way to represent the direction and relative strength of a magnetic field.
- Isolated magnetic poles are not observed in ordinary magnets.
3. Bar Magnet as an Equivalent Solenoid
A current-carrying solenoid produces a magnetic field pattern that, at a qualitative level, resembles the field of a bar magnet. This leads to the equivalent-solenoid model of a bar magnet.
| Bar magnet | Equivalent-solenoid idea |
|---|---|
| Has north and south poles | A current-carrying solenoid also has two magnetic ends |
| Produces a dipole-like field pattern | The solenoid produces a similar dipole-like external field |
| Magnetic moment has a definite direction | Solenoid magnetic moment follows the right-hand rule |
For the current CBSE syllabus, this equivalence is a qualitative treatment. The goal is to understand the physical picture rather than memorise an extended derivation.
4. Magnetic Field Lines
Magnetic field lines are a visual representation of the magnetic field. The tangent to a field line at a point gives the direction of the magnetic field at that point.
Important properties
- Outside a bar magnet, field lines are conventionally drawn from the north pole toward the south pole.
- Inside the magnet, they continue from south toward north, forming closed loops.
- Field lines do not normally intersect each other because the magnetic field at a point has a unique direction.
- Closer field lines indicate a stronger field in the usual field-line representation.
- A compass needle aligns itself with the local magnetic field direction.
5. Magnetic Field of a Bar Magnet — Qualitative Picture
Axial and perpendicular (equatorial) positions
For a bar magnet, the magnetic field can be discussed at different positions around the magnet. Two important directions are the axial direction and the perpendicular or equatorial direction.
Axial position
A point on the line passing through the two poles of the magnet is said to lie on the axial line. Imagine extending the magnet's N–S line outward from either pole.
Exam idea: identify the point as being on the same line as the magnetic axis and describe the field direction using the field-line pattern.
Perpendicular / equatorial position
A point on the perpendicular bisector of the magnet is in the equatorial region. Imagine drawing a line through the centre of the magnet at right angles to its magnetic axis.
Exam idea: recognise that the field direction here is determined by the combined effect of the two poles and is different from the axial case.
What should you learn for CBSE 2026–27?
- Know what axial and perpendicular/equatorial positions mean.
- Understand that the field direction depends on the position relative to the magnet.
- Use magnetic field-line diagrams to reason about direction and relative field strength.
- Keep the treatment qualitative: the current CBSE syllabus specifies qualitative magnetic-field intensity along the axis and perpendicular to the axis.
6. Magnetic Dipole in a Uniform Magnetic Field
Magnetic dipole moment: what it tells you
The magnetic dipole moment describes the strength and orientation of a magnetic dipole. For a current-carrying coil, the useful relationship is m = NIA, where N is the number of turns, I is current and A is the area of the coil.
This creates a natural bridge from Chapter 4: the current in a loop produces magnetic effects; in Chapter 5, the resulting magnetic dipole is used to understand torque, alignment and magnetic behaviour.
A bar magnet placed in a uniform magnetic field behaves as a magnetic dipole. The magnetic field exerts forces on its two poles. In a uniform field, these forces are equal in magnitude and opposite in direction, so the net force can be zero, but the forces can form a couple and produce a torque.
Torque — qualitative understanding
The torque tends to rotate the magnetic dipole so that its magnetic moment aligns with the external magnetic field.
Here m is the magnitude of magnetic dipole moment, B is the magnetic field, and θ is the angle between the magnetic moment and the field. For the current CBSE syllabus, the torque treatment is qualitative, so focus on the direction, alignment tendency and special cases.
| Orientation | Torque | Meaning |
|---|---|---|
| m parallel to B | Zero | Dipole is aligned with the field. |
| m antiparallel to B | Zero | Unstable orientation; a small displacement tends to rotate it away. |
| m perpendicular to B | Maximum | Strongest turning tendency. |
7. Magnetic Properties of Materials
When a material is placed in an external magnetic field, its microscopic magnetic moments respond to the field. The resulting behaviour is used to classify materials into three broad groups in the CBSE syllabus: diamagnetic, paramagnetic and ferromagnetic.
| Property / useful comparison | Diamagnetic | Paramagnetic | Ferromagnetic |
|---|---|---|---|
| Response to external field | Weakly repelled | Weakly attracted | Strongly attracted |
| Magnetic susceptibility | Small and negative | Small and positive | Large and positive |
| Relative permeability | Slightly less than 1 | Slightly greater than 1 | Much greater than 1 in strongly magnetised conditions |
| Typical examples | Bismuth, copper, water | Aluminium, platinum, oxygen | Iron, cobalt, nickel |
| Effect of removing field | Very weak induced response disappears | Weak magnetisation largely disappears | Strong magnetisation may persist depending on the material and history |
Note: The examples above are representative textbook examples; the important exam skill is to recognise the defining response of each class rather than memorise an unlimited list.
8. Diamagnetic Substances
Diamagnetic materials develop a magnetic response that opposes the applied magnetic field. They are therefore weakly repelled by a magnetic field.
- Magnetic susceptibility is small and negative.
- Relative permeability is slightly less than unity.
- The induced magnetic moment is opposite to the applied field direction.
9. Paramagnetic Substances
Paramagnetic materials are weakly attracted by an external magnetic field. Their microscopic magnetic moments tend to show a preferential alignment with the applied field, although thermal motion prevents complete alignment.
- Magnetic susceptibility is small and positive.
- Relative permeability is slightly greater than unity.
- The magnetic response is generally temperature dependent.
10. Ferromagnetic Substances
Ferromagnetic materials show a much stronger magnetic response than dia- or paramagnetic substances. Their microscopic magnetic moments can align strongly, giving rise to large magnetisation.
- Magnetic susceptibility is large and positive.
- They can be strongly attracted by a magnetic field.
- Magnetic domains provide a useful microscopic picture of their strong magnetic behaviour.
- Temperature strongly affects ferromagnetic behaviour.
11. Magnetisation of Materials
Physical meaning
Magnetisation describes the magnetic dipole moment developed per unit volume of a magnetised material. It gives a macroscopic picture of how strongly the material responds through the alignment or induced behaviour of its microscopic magnetic moments.
The SI unit of magnetisation is A m−1.
M = magnetic dipole moment / volumeMicroscopic → macroscopic picture
Inside a material, atoms or molecules can contribute tiny magnetic moments. When their overall response produces a net magnetic moment per unit volume, the material is said to be magnetised.
Why it matters
Magnetisation helps connect the microscopic magnetic response of a material with the observable magnetic behaviour discussed for diamagnetic, paramagnetic and ferromagnetic substances.
12. Effect of Temperature on Magnetic Properties
Temperature changes the magnetic response of matter because thermal motion competes with the ordering of microscopic magnetic moments.
| Material class | Temperature-related idea to remember |
|---|---|
| Diamagnetic | The magnetic response is comparatively weak and is not explained by permanent alignment of magnetic moments. |
| Paramagnetic | Thermal agitation opposes alignment, so the magnetic response depends on temperature. |
| Ferromagnetic | Increasing temperature weakens magnetic ordering; above the Curie temperature, ferromagnetic behaviour is lost and the material becomes approximately paramagnetic. |
13. What Older Resources May Show — Read with Care
14. Assessment-Aware Extension — Useful, but Not Core Syllabus
Some current school/assessment resources may use terms such as magnetic susceptibility (χ), relative permeability (μr), magnetic intensity (H) or the qualitative relation between B, H and M. These are useful for deeper understanding and can appear in assessment-aware practice, but they are not listed as separate compulsory Chapter 5 items in the CBSE 2026–27 curriculum wording.
Rule: learn the prescribed qualitative core first. Treat extended material-parameter formulae as enrichment rather than replacing the syllabus-focused preparation on this page.
15. Chapter 5 at a Glance
| Topic | What to learn | Treatment |
|---|---|---|
| Bar magnet | Poles, dipole idea, basic behaviour | Conceptual |
| Equivalent solenoid | Qualitative magnetic-field analogy | Qualitative |
| Dipole field | Axial and perpendicular positions; field direction | Qualitative |
| Dipole in a field | Torque, alignment and special orientations | Qualitative + useful relationship |
| Magnetic field lines | Direction, continuity and relative strength | Conceptual |
| Magnetic materials | Diamagnetic, paramagnetic and ferromagnetic behaviour | Conceptual |
| Magnetisation | Meaning, definition and SI unit | Conceptual |
| Temperature | Effect on magnetic behaviour | Conceptual |
16. Formula & Relationship Map
Magnetic dipole moment of a current loop:
Torque on a magnetic dipole in a magnetic field:
Magnetisation:
Important: Chapter 5's current CBSE treatment is deliberately qualitative for the bar-magnet field, equivalent-solenoid picture and dipole torque. Do not turn this page into a formula-dumping exercise.
17. Common Exam Traps
18. How to Study Chapter 5
- First: understand the bar magnet and magnetic field-line picture.
- Second: connect the bar magnet with the equivalent-solenoid model.
- Third: understand torque and the stable/unstable orientations of a magnetic dipole.
- Fourth: master the comparison of diamagnetic, paramagnetic and ferromagnetic materials.
- Fifth: revise magnetisation and the qualitative effect of temperature.
- Finally: practise MCQs, important questions, numericals where applicable, case-based questions and the chapter test.
Frequently Asked Questions
What is Magnetism and Matter in Class 12 Physics?
It is Chapter 5 of Class 12 Physics and covers bar magnets, magnetic field lines, magnetic dipoles, magnetic materials, magnetisation and temperature effects within the current CBSE 2026–27 scope.
What is Chapter 5 of Class 12 Physics?
Chapter 5 is Magnetism and Matter.
What are the main topics in Magnetism and Matter?
The current syllabus includes the bar magnet, its qualitative equivalence to a solenoid, qualitative magnetic field intensity along and perpendicular to the axis, torque on a magnetic dipole in a uniform magnetic field, magnetic field lines, magnetic materials, magnetisation and temperature effects.
What is a magnetic dipole?
A magnetic dipole is a system with magnetic-pole behaviour characterised by a magnetic dipole moment. A bar magnet is treated as a magnetic dipole in this chapter.
What is a bar magnet as an equivalent solenoid?
A bar magnet can be represented qualitatively by a current-carrying solenoid because their magnetic-field patterns have corresponding features.
What are diamagnetic, paramagnetic and ferromagnetic substances?
They are three broad classes of magnetic materials distinguished by how they respond to an applied magnetic field. Their characteristic responses and examples are compared in the material-classification sections above.
What is magnetisation?
Magnetisation is the magnetic dipole moment developed per unit volume of a material. Its SI unit is A m−1.
How does temperature affect magnetic properties?
Temperature changes the magnetic behaviour of materials. In particular, ferromagnetic behaviour is associated with a critical temperature called the Curie temperature, above which the characteristic ferromagnetic ordering is lost.
Where can I find Magnetism and Matter Class 12 Physics PYQs?
Use the Magnetism and Matter Class 12 Physics PYQs page for chapter-wise previous-year practice and solutions.
Where can I find the Magnetism and Matter Class 12 Physics chapter test?
Use the Class 12 Physics Chapter 5 Test for a timed final check after completing the chapter resources.
How many marks are fixed for Chapter 5?
CBSE assigns 17 marks to Unit III: Magnetic Effects of Current and Magnetism, which contains Chapters 4 and 5 together. The curriculum does not prescribe a separate fixed mark allocation for Chapter 5 alone.
19. Chapter 5 Study Resources
Complete Chapter 5 resource path: All major companion resources are now published, so students can move from learning to practice without placeholder links.
Recommended sequence: Read the Notes → practise Important Questions → test concepts with MCQs → solve Numericals → practise Case-Based Questions → attempt Assertion–Reason → revise PYQs → use the Formula Sheet → finish with the Chapter Test.
Chapter 4 connection: Moving Charges and Magnetism Class 12 Physics Notes explains how moving charges and currents produce magnetic fields and experience magnetic forces; Chapter 5 builds on that foundation by studying magnets and magnetic matter.
20. Continue the Class 12 Physics Chapter Sequence
Chapter 4: Moving Charges and Magnetism
Chapter 3: Current Electricity
Chapter 2: Electrostatic Potential and Capacitance
Chapter 1: Electric Charges and Fields
21. Final Exam-Readiness Check
✓ I can explain the basic properties of a bar magnet.
✓ I can describe a bar magnet as an equivalent solenoid qualitatively.
✓ I can state the key properties and direction of magnetic field lines.
✓ I can explain torque on a magnetic dipole and distinguish stable from unstable orientation.
✓ I can distinguish diamagnetic, paramagnetic and ferromagnetic substances.
✓ I can explain magnetisation and its unit.
✓ I can explain the qualitative effect of temperature on magnetic properties.
✓ I can avoid importing topics that are outside the current CBSE 2026–27 Chapter 5 scope.
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