PhysicsCBSE Class 12 · Chapter 5

Magnetism and Matter Class 12: Notes, Key Ideas and Solved Questions

Updated 14 October 2026 · Fact-checked

Magnetism and Matter is Chapter 5 of CBSE Class 12 Physics. It treats the bar magnet as an equivalent solenoid and a magnetic dipole (qualitatively), magnetic field lines, magnetisation and magnetic intensity, and the three kinds of magnetic material, diamagnetic, paramagnetic and ferromagnetic, with examples and the effect of temperature on them.

What Magnetism and Matter is about

Chapter 4 showed that a current loop behaves like a tiny magnet. This chapter starts from the other end: the familiar bar magnet. You see that a bar magnet behaves like a solenoid carrying current, that its field lines form closed loops, and that its field and the torque on it in a uniform field have the same form as those of an electric dipole, with $p$ replaced by $m$ . For 2026-27 all of this is treated qualitatively: know the results and the pictures, not the mathematical derivations.

The second half is about matter in a magnetic field. A material placed in a field becomes magnetised; its magnetisation $M$ (magnetic moment per unit volume) adds to the applied magnetic intensity $H$ , so $B = μ_{0} (H + M)$ with $M = χ H$ . The sign and size of the susceptibility χ sort materials into diamagnetic (small negative χ, weakly repelled), paramagnetic (small positive χ, weakly attracted) and ferromagnetic (very large positive χ, strongly attracted). Heating weakens paramagnetism and ferromagnetism.

Earth's magnetism, Curie's law, the Curie temperature in detail, hysteresis, and permanent magnets and electromagnets are not in the 2026-27 syllabus. This is a short, mostly 1- and 2-mark chapter: in our question bank it has 12 questions, appearing in 4 of the 8 board papers from 2023 to 2026, mostly MCQs and assertion-reason items on classifying materials.

Weightage: This chapter is part of Units III and IV, Magnetic Effects of Current and Magnetism; Electromagnetic Induction and Alternating Currents, which carry 17 of the 70 theory marks together with Moving Charges and Magnetism, Electromagnetic Induction and Alternating Current.Source: CBSE Physics syllabus 2026-27, Units III and IV Magnetic Effects of Current and Magnetism; Electromagnetic Induction and Alternating Currents

In real board papers: asked in 4 of the 8 board papers we hold (2023 to 2026), on average 0.6 marks per paper. See the questions

Key concepts

The bar magnet and magnetic field lines

NCERT section 5.2 and 5.2.1

A bar magnet has two poles, north and south, near its ends. Like poles repel and unlike poles attract. A freely suspended bar magnet settles roughly along the geographic north-south direction.

Isolated poles do not exist. If you cut a bar magnet in two, you get two smaller magnets, each with its own north and south pole. There are no magnetic monopoles.

Field lines of a bar magnet:

They form continuous closed loops: outside the magnet they run from the north pole to the south pole, and inside the magnet from south to north. (Electric field lines, in contrast, start and end on charges.)
The tangent at any point gives the direction of $B$ .
The closer the lines, the stronger the field.
Two field lines never cross.

Because the lines are closed loops, as many lines leave any closed surface as enter it, so the net magnetic flux through any closed surface is zero (Gauss's law for magnetism, $\oint B \cdot d S = 0$ ).

Worked example

A bar magnet is cut into two equal halves along a line perpendicular to its length. (a) Can you get an isolated north pole this way? (b) How does the magnetic moment of each half compare with that of the original? [2 marks]

Try it first, then show the solutionSolution

(a) No. Each half develops a new pole at the cut and becomes a complete magnet with its own N and S poles, because magnetic monopoles do not exist.
(b) Each half has the same pole strength but half the length, so its magnetic moment (pole strength × length) is half the original.

Answer: (a) No, each piece is a complete magnet. (b) Each half has half the original magnetic moment.

Bar magnet as an equivalent solenoid (qualitative)

NCERT section 5.2.2

Sprinkle iron filings round a bar magnet and round a current-carrying solenoid, and the patterns look the same. The solenoid's turns behave like a stack of current loops, each a magnetic dipole; together they act like one bar magnet, with one end a north pole and the other a south pole (fixed by the right-hand rule).

This suggests that the magnetism of a bar magnet comes from tiny circulating currents inside it, and that a bar magnet can be treated as a solenoid with an equivalent magnetic moment $m$ pointing from its S pole to its N pole. The syllabus asks for this idea qualitatively; the mathematical comparison is not required.

The far field of either one has the same form as that of an electric dipole:

On the axis: $B = \frac{μ _{0}}{4 π} \frac{2 m}{r ^{3}}$ , along $m$ .
On the equatorial line: $B = \frac{μ _{0}}{4 π} \frac{m}{r ^{3}}$ , opposite to $m$ .

So at the same large distance the axial field is twice the equatorial field, and both fall off as $\frac{1}{r ^{3}}$ .

Worked example

A short bar magnet has magnetic moment $0.5 A m^{2}$ . Using the dipole results, find the field at 10 cm from its centre (a) on its axis, (b) on its equatorial line. [2 marks]

Try it first, then show the solutionSolution

$\frac{μ _{0}}{4 π} = 1 0^{- 7}$ ; $r^{3} = (0.1)^{3} = 1 0^{- 3} m^{3}$
(a) $B_{a x ia l} = 1 0^{- 7} \times \frac{2 \times 0.5}{1 0 ^{- 3}} = 1 \times 1 0^{- 4} T$ , along $m$ (S to N)
(b) $B_{e q} = 1 0^{- 7} \times \frac{0.5}{1 0 ^{- 3}} = 5 \times 1 0^{- 5} T$ , opposite to $m$

Answer: (a) $1 \times 1 0^{- 4} T$ (b) $5 \times 1 0^{- 5} T$

A magnetic dipole in a uniform field (qualitative)

NCERT section 5.2.3 and 5.2.4

A bar magnet (or current loop) of moment $m$ in a uniform field $B$ feels no net force (the forces on its two poles are equal and opposite) but a torque that tries to line $m$ up with $B$ :

$τ = m \times B, τ = m B sin θ$

Its potential energy is $U = - m \cdot B = - m B cos θ$ : lowest (stable equilibrium) when $m$ is along $B$ , highest (unstable) when it is opposite. A compass needle works this way: it turns until its moment points along the field.

Electrostatic analogue. Every result for an electric dipole carries over with $p \to m$ , $E \to B$ and $\frac{1}{ε _{0}} \to μ_{0}$ . The syllabus asks for these ideas qualitatively.

Worked example

A short magnet of moment $0.4 J T^{- 1}$ is placed at $6 0^{\circ}$ to a uniform field of 0.2 T. Find the torque on it and say which way it tends to turn. [2 marks]

Try it first, then show the solutionSolution

$τ = m B sin θ = 0.4 \times 0.2 \times sin 6 0^{\circ} = 0.08 \times 0.866$
$τ \approx 6.9 \times 1 0^{- 2} N m$
It turns so as to reduce θ, bringing $m$ into line with $B$ .

Answer: About 0.069 N m, turning the magnet towards the field direction.

Magnetisation and magnetic intensity

NCERT section 5.4

In matter, the electrons' orbital and spin motions give atoms tiny magnetic moments. In a field these can line up (or be induced) and the material becomes magnetised.

Magnetisation $M$ : net magnetic moment per unit volume, $M = \frac{m _{n e t}}{V}$ ; unit A m⁻¹.
Magnetic intensity $H$ : the part of the field set up by external currents, $H = \frac{B _{0}}{μ _{0}}$ . In a solenoid, $H = n I$ . Unit A m⁻¹.
The total field inside the material is $B = μ_{0} (H + M)$ .
For most materials $M = χ H$ , where χ (dimensionless) is the magnetic susceptibility: how strongly the material responds.
Then $B = μ_{0} (1 + χ) H = μ_{0} μ_{r} H = μ H$ , with relative permeability $μ_{r} = 1 + χ$ and permeability $μ = μ_{0} μ_{r}$ .

Worked example

A solenoid with 500 turns per metre carries 3 A and has a core of relative permeability 600. Find H, B, χ and M inside the core. ( $μ_{0} = 4 π \times 1 0^{- 7} T m A^{- 1}$ ) [3 marks]

Try it first, then show the solutionSolution

$H = n I = 500 \times 3 = 1500 A m^{- 1}$
$B = μ_{r} μ_{0} H = 600 \times 4 π \times 1 0^{- 7} \times 1500 \approx 1.13 T$
$χ = μ_{r} - 1 = 599$
$M = χH = 599 \times 1500 \approx 8.99 \times 1 0^{5} A m^{- 1}$

Answer: H = 1500 A m⁻¹; B ≈ 1.13 T; χ = 599; M ≈ $9.0 \times 1 0^{5} A m^{- 1}$

Diamagnetism

NCERT section 5.5.1

Diamagnetic substances are magnetised opposite to the applied field and are weakly repelled by a magnet; they tend to move from stronger to weaker parts of a field.

χ is small and negative; $0 \leq μ_{r} < 1$ .
Field lines are pushed out of the material: the field inside is slightly weaker than outside.
Cause: in these atoms the electron moments cancel; an applied field speeds up electrons orbiting one way and slows those orbiting the other way, giving a net moment opposite to the field.
Examples: bismuth, copper, lead, silicon, nitrogen (at STP), water and sodium chloride.
Superconductors are perfect diamagnets: $χ = - 1$ , $μ_{r} = 0$ , and they expel the field completely (the Meissner effect).
Diamagnetism is present in all materials but is usually masked when other kinds are present. It hardly depends on temperature.

Worked example

A material has susceptibility $- 1.6 \times 1 0^{- 5}$ . (a) Is it diamagnetic or paramagnetic? (b) Find its relative permeability. (c) What happens when a rod of it is brought near a strong magnet? [2 marks]

Try it first, then show the solutionSolution

(a) Small negative χ: diamagnetic.
(b) $μ_{r} = 1 + χ = 1 - 0.000016 = 0.999984$
(c) It is weakly repelled, moving towards the weaker part of the field.

Answer: (a) Diamagnetic (b) $μ_{r} = 0.999984$ (c) weakly repelled

Paramagnetism

NCERT section 5.5.2

Paramagnetic substances are weakly magnetised along the applied field and weakly attracted by a magnet; they tend to move from weaker to stronger parts of a field.

χ is small and positive; $μ_{r}$ is slightly more than 1.
Field lines crowd slightly into the material.
Cause: each atom has a permanent magnetic moment, but thermal motion points them in random directions. An applied field lines them up partly.
Examples: aluminium, sodium, calcium, oxygen (at STP) and copper chloride.
Effect of temperature: heating increases the random thermal motion, which disturbs the alignment, so the magnetisation (and χ) decreases as temperature rises; cooling strengthens it.

Worked example

A sample of a paramagnetic salt is magnetised in a fixed field at room temperature. What happens to its magnetisation if (a) it is cooled, (b) the field is made stronger? Explain. [2 marks]

Try it first, then show the solutionSolution

(a) Cooling reduces thermal agitation, so more atomic moments stay aligned with the field: magnetisation increases.
(b) A stronger field lines up more of the moments against the thermal disorder: magnetisation increases.

Answer: It increases in both cases: less thermal disorder (a) or stronger aligning field (b).

Ferromagnetism

NCERT section 5.5.3

Ferromagnetic substances are strongly magnetised along the field and strongly attracted by a magnet.

χ is very large and positive ( $μ_{r}$ can be in the thousands).
Field lines crowd strongly into the material.
Cause: neighbouring atomic moments line up with each other spontaneously over regions called domains (each perhaps a millimetre across, containing a huge number of atoms). In an unmagnetised piece the domains point in random directions. An applied field makes the domains aligned with it grow and others rotate, giving a large net magnetisation.
Examples: iron, cobalt, nickel and gadolinium.
Some ferromagnets keep much of their magnetisation when the field is removed; others (such as soft iron) lose it easily.
Effect of temperature: heating disturbs the alignment; above a certain temperature the domain structure breaks down and the substance becomes paramagnetic. (The detailed treatment of this transition temperature and of hysteresis is not in the 2026-27 syllabus.)

Worked example

Three samples have relative permeabilities of 0.9998, 1.0002 and 1500. Identify each type of material and say how each behaves near a strong magnet. [2 marks]

Try it first, then show the solutionSolution

0.9998: $χ = - 0.0002 < 0$ , so diamagnetic: weakly repelled.
1.0002: $χ = + 0.0002$ , small positive, so paramagnetic: weakly attracted.
1500: $χ = 1499$ , very large, so ferromagnetic: strongly attracted.

Answer: Diamagnetic (weakly repelled), paramagnetic (weakly attracted), ferromagnetic (strongly attracted)

Physics in real life: Magnetism and Matter

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Ferromagnetic and other materials

Suppose a scrap-recycling yard uses a strong electromagnet on a crane to sort a mixed pile of iron, aluminium and copper scrap.

Which metals will the magnet lift? Explain using the type of magnetism of each.

Try it first, then show the solutionSolution

Iron is ferromagnetic: very large χ, strongly attracted, so the magnet lifts it.
Aluminium is paramagnetic: tiny positive χ, attracted only very weakly, far too little to overcome its weight.
Copper is diamagnetic: tiny negative χ, very weakly repelled, so it stays behind.

Answer: Only the iron is lifted; aluminium and copper are left in the pile.

Memory hook: Ferro flies to the magnet; para barely notices; dia quietly backs away.

Field of a magnetic dipole

Suppose you hold a small, strong magnet with magnetic moment $2 A m^{2}$ near a sensitive compass, with the compass on the magnet's axis.

Find the magnet's field at the compass when it is 10 cm away and when it is 20 cm away, both on the axis.

Try it first, then show the solutionSolution

At 10 cm: $B = 1 0^{- 7} \times \frac{2 \times 2}{( 0.1 ) ^{3}} = 1 0^{- 7} \times 4000 = 4 \times 1 0^{- 4} T$
At 20 cm: the distance doubles, so B falls by $2^{3} = 8$ : $5 \times 1 0^{- 5} T$
A dipole field fades quickly with distance, as $1/ r^{3}$ .

Answer: $4 \times 1 0^{- 4} T$ at 10 cm; $5 \times 1 0^{- 5} T$ at 20 cm.

Memory hook: Double the distance, one eighth the field: dipoles fade fast.

Superconductors as perfect diamagnets

Imagine a small disc of superconducting material cooled with liquid nitrogen, with a small magnet placed above it. The magnet floats in the air.

Use the idea of diamagnetism to explain why the magnet floats.

Try it first, then show the solutionSolution

A superconductor below its transition temperature is a perfect diamagnet: $χ = - 1$ , so it expels the magnet's field completely.
Its induced magnetisation opposes the magnet's field, so the superconductor repels the magnet.
The repulsion balances the magnet's weight, so it hovers.

Answer: The perfectly diamagnetic superconductor repels the magnet strongly enough to balance its weight.

Memory hook: Perfect diamagnet, perfect push: χ = −1 holds the magnet up.

Topics in this chapter

Magnetism and Matter formula sheet

Axial field of a short magnet (qualitative): $B_{a x ia l} = \frac{μ _{0}}{4 π} \frac{2 m}{r ^{3}}$
Equatorial field of a short magnet (qualitative): $B_{e q} = \frac{μ _{0}}{4 π} \frac{m}{r ^{3}}$; Opposite to $m$ ; half the axial value at the same r.
Torque and energy of a magnetic dipole: $τ = m \times B, U = - m \cdot B$
Gauss's law for magnetism: $\oint B \cdot d S = 0$
Magnetisation: $M = \frac{m _{n e t}}{V}$; Unit A m⁻¹.
Magnetic intensity: $H = \frac{B _{0}}{μ _{0}}, H = n I (solenoid)$
Total field in matter: $B = μ_{0} (H + M)$
Susceptibility: $M = χ H$
Relative permeability: $μ_{r} = 1 + χ, μ = μ_{0} μ_{r}, B = μ H$

Magnetism and Matter: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Field lines of a bar magnet and of a solenoid

Comparing a bar magnet with a solenoid (1-2 marks).

Draw

Draw a rectangle for the magnet with N at one end and S at the other.
Draw closed loops leaving N, curving round outside and entering S; continue each line inside the magnet from S back to N.
Beside it, draw a solenoid (a row of loops) with the same pattern of lines, and mark which end acts as N using the right-hand rule.

Label

N and S poles
Field lines (closed loops)
Solenoid with current direction
Equivalent N and S ends

Watch out: Arrows outside go N to S; inside, S to N. Never let lines start or stop at a pole.

Dia-, para- and ferromagnetic samples in a uniform field

"Show the behaviour of magnetic field lines" (2 marks).

Draw

Draw equally spaced parallel field lines across the page.
Diamagnetic: place a circle (sample) and bend the lines around it, with fewer lines passing through.
Paramagnetic: bend the lines slightly into the sample so a few more pass through it.
Ferromagnetic: bend many lines sharply into the sample so it is crowded with lines.

Label

Uniform field B
Diamagnetic sample
Paramagnetic sample
Ferromagnetic sample

Watch out: Label each sample with the sign of χ so the examiner sees you know why the lines bend.

How the board asks Magnetism and Matter

The question patterns to expect, and the method that works for each.

Question type	How it is asked	Method
Classify a material	MCQs giving χ or $μ_{r}$ , or naming substances (bismuth, aluminium, nickel), and asking the type or behaviour.	Sign and size of χ: small negative = dia, small positive = para, very large positive = ferro. Learn two examples of each.
Field-line diagrams in materials	Draw how field lines behave when a diamagnetic or paramagnetic sample is placed in a uniform field.	Diamagnetic: lines bend away and are fewer inside. Paramagnetic: lines bend slightly into the sample. Ferromagnetic: lines crowd strongly into it.
Assertion-reason on properties	Statements about superconductors, temperature effects, atomic moments, closed field lines.	Check each statement against the cause of that kind of magnetism (induced, permanent random, domains).
M, H, B, χ numericals	A solenoid with a core of given $μ_{r}$ ; find H, B, M or χ.	H = nI first, then $B = μ_{0} μ_{r} H$ and $M = (μ_{r} - 1) H$ .
Bar magnet as a dipole (qualitative)	Compare axial and equatorial fields, direction of torque, stable and unstable positions, cutting a magnet.	Use the electric-dipole analogy; quote results rather than derive them.

Tricks to remember Magnetism and Matter

Short memory aids. Say each one aloud once, then use it on a question the same day.

Dia = Departs, Para = Pulled a little, Ferro = Firmly pulled
Diamagnetic materials depart (repelled), paramagnetic are pulled a little, ferromagnetic are firmly pulled.
Use it when: Behaviour near a magnet.
Signs of χ
Dia: minus and tiny. Para: plus and tiny. Ferro: plus and huge. μr is 1 + χ.
Use it when: Classifying from χ or μr.
Example lists: 'Bi Cu Pb' and 'Al Na Ca' and 'Fe Co Ni Gd'
Dia: bismuth, copper, lead. Para: aluminium, sodium, calcium. Ferro: iron, cobalt, nickel, gadolinium.
Use it when: One-mark example questions.
Heat scrambles
Heat jostles atoms and scrambles alignment: paramagnetism weakens with temperature, ferromagnetism is lost above a certain temperature, diamagnetism barely cares.
Use it when: Effect-of-temperature questions.
B = μ₀(H + M)
Total field = what the currents give (H) + what the material adds (M), all times μ₀.
Use it when: Numericals on solenoids with cores.

Magnetism and Matter: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Example 1: Permeability less than free space · 1 mark · MCQBoard level

Which of these has a permeability less than that of free space?
(a) aluminium
(b) nickel
(c) bismuth
(d) sodium

Try it first, then show the solutionSolution

$μ < μ_{0}$ means $μ_{r} < 1$ , i.e. diamagnetic. Bismuth is diamagnetic; aluminium and sodium are paramagnetic; nickel is ferromagnetic.

Answer: (c) bismuth

Example 2: Superconductor and field · 1 mark · Assertion-reasonBoard level

Assertion (A): A superconductor expels a magnetic field from its interior.
Reason (R): A superconductor is a perfect diamagnet with susceptibility −1.
(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

Try it first, then show the solutionSolution

With χ = −1, $M = - H$ and $B = μ_{0} (H + M) = 0$ inside, so the field is expelled. Both true; R explains A.

Answer: (a)

Example 3: Field lines through dia- and paramagnetic samples · 2 marks · Very short answerHarder board level

A sample is placed in a uniform magnetic field. Field lines bend away from it and the field inside it becomes slightly weaker. (a) Identify the type of material and give one example. (b) In which direction would it move in a non-uniform field? [2 marks]

Try it first, then show the solutionSolution

(a) Lines pushed out and a weaker field inside mean $μ_{r} < 1$ : diamagnetic, for example bismuth or copper.
(b) It moves from the stronger part of the field to the weaker part (it is repelled).

Answer: (a) Diamagnetic, e.g. bismuth (b) towards the weaker field

Example 4: Core inside a solenoid · 3 marks · Short answerHarder board level

A solenoid with 800 turns per metre carries 2.5 A. Its core has relative permeability 400. Find (a) H, (b) B, (c) the susceptibility, (d) the magnetisation. What kind of material is the core? [3 marks]

Try it first, then show the solutionSolution

(a) $H = n I = 800 \times 2.5 = 2000 A m^{- 1}$
(b) $B = μ_{0} μ_{r} H = 4 π \times 1 0^{- 7} \times 400 \times 2000 \approx 1.01 T$
(c) $χ = μ_{r} - 1 = 399$ ; (d) $M = χH = 399 \times 2000 \approx 7.98 \times 1 0^{5} A m^{- 1}$
A very large positive χ means a ferromagnetic core.

Answer: H = 2000 A m⁻¹; B ≈ 1.01 T; χ = 399; M ≈ $8.0 \times 1 0^{5} A m^{- 1}$ ; ferromagnetic.

Example 5: Short magnet: axial and equatorial fields and torque · 3 marks · Short answerHarder board level

A short bar magnet has magnetic moment $0.5 A m^{2}$ . (a) Find its field at 20 cm on the axis and on the equatorial line. (b) If it is placed in a uniform field of 0.4 T at $3 0^{\circ}$ to the field, find the torque and the direction in which it turns. [3 marks]

Try it first, then show the solutionSolution

(a) $r^{3} = (0.2)^{3} = 8 \times 1 0^{- 3} m^{3}$ ; $B_{a x ia l} = 1 0^{- 7} \times \frac{2 \times 0.5}{8 \times 1 0 ^{- 3}} = 1.25 \times 1 0^{- 5} T$ ; $B_{e q} = \frac{B _{a x ia l}}{2} = 6.25 \times 1 0^{- 6} T$
(b) $τ = m B sin θ = 0.5 \times 0.4 \times 0.5 = 0.1 N m$
The torque turns the magnet so that $m$ moves towards $B$ (θ decreases).

Answer: (a) $1.25 \times 1 0^{- 5} T$ and $6.25 \times 1 0^{- 6} T$ (b) 0.1 N m, turning $m$ into line with $B$

Example 6: Comparing magnetic materials · 5 marks · Long answerHarder board level

(a) Define magnetisation, magnetic intensity and susceptibility, and write the relation between B, H and M. (b) Compare diamagnetic, paramagnetic and ferromagnetic materials (χ, μr, behaviour, cause). (c) A material has $χ = 2.0 \times 1 0^{- 5}$ . In a field of intensity $5 \times 1 0^{4} A m^{- 1}$ , find its magnetisation and classify it. [5 marks]

Try it first, then show the solutionSolution

(a) M: net magnetic moment per unit volume. H: field due to external currents divided by $μ_{0}$ (H = nI in a solenoid). χ: M/H. $B = μ_{0} (H + M)$ .
(b) Diamagnetic: χ small negative, $μ_{r} < 1$ , weakly repelled, moment induced opposite to the field.
Paramagnetic: χ small positive, $μ_{r}$ slightly > 1, weakly attracted, permanent atomic moments partly aligned.
Ferromagnetic: χ very large, $μ_{r} ≫ 1$ , strongly attracted, domains of aligned moments.
(c) $M = χH = 2.0 \times 1 0^{- 5} \times 5 \times 1 0^{4} = 1.0 A m^{- 1}$ ; small positive χ, so paramagnetic.

Answer: Definitions as above; M = 1.0 A m⁻¹; paramagnetic.

Example 7: Liquids in a U-tube between magnet poles · 2 marks · Very short answerHOTS / competency

One arm of a U-tube is placed between the poles of a strong electromagnet, so that the liquid surface in that arm lies in the strong field. What happens to the level in that arm when the magnet is switched on if the liquid is (a) paramagnetic, (b) diamagnetic? Explain. [2 marks]

Try it first, then show the solutionSolution

(a) A paramagnetic liquid is drawn towards the stronger field, so the level in the arm between the poles rises.
(b) A diamagnetic liquid is pushed towards the weaker field, so the level in that arm falls.

Answer: (a) It rises (b) it falls.

Example 8: Temperature and a ferromagnet · 2 marks · Very short answerHOTS / competency

An iron nail is held by a magnet. The nail is then heated strongly with a burner while it is still near the magnet. After some time it falls off. Explain this using the domain picture, and say what kind of magnetic material the hot nail behaves as. [2 marks]

Try it first, then show the solutionSolution

Iron is ferromagnetic: neighbouring atomic moments line up in domains, and the magnet's field aligns the domains, so the nail is strongly attracted.
Strong heating increases thermal agitation, which breaks down the alignment within the domains. Above a certain temperature the ferromagnetic order is lost.
The hot nail then behaves as a paramagnet, attracted only very weakly, so its weight makes it fall.

Answer: Heating destroys the domain alignment; the hot nail becomes paramagnetic, is only weakly attracted, and falls.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 4-mark question split into 1 + 1 + 1 + 1 marks.

Sorting unknown samples

Suppose a student measures the magnetic susceptibility of three unknown samples at room temperature: sample P has $χ = - 1.5 \times 1 0^{- 5}$ , sample Q has $χ = + 2.1 \times 1 0^{- 5}$ and sample R has $χ = + 3000$ .

(i) · 1 mark
Which sample is diamagnetic?
Answer
Answer: P
Only P has a small negative susceptibility.
(ii) · 1 mark
Which sample is most strongly attracted by a magnet?
Answer
Answer: R
R has a very large positive χ: ferromagnetic.
(iii) · 1 mark
Find the relative permeability of Q.
Answer
Answer: 1.000021
$μ_{r} = 1 + χ = 1 + 0.000021$
(iv) · 1 mark
If Q is cooled, will its susceptibility rise or fall?
Answer
Answer: Rise
Q is paramagnetic; cooling reduces thermal disorder, so the atomic moments align more easily.

A cored solenoid

Suppose a solenoid has 1000 turns per metre and carries a current of 1.5 A. It is filled with a core of relative permeability 800. Take $μ_{0} = 4 π \times 1 0^{- 7} T m A^{- 1}$ .

(i) · 1 mark
Find the magnetic intensity H inside.
Answer
Answer: 1500 A m⁻¹
$H = n I = 1000 \times 1.5$
(ii) · 1 mark
Find B inside the core.
Answer
Answer: About 1.51 T
$B = μ_{0} μ_{r} H = 4 π \times 1 0^{- 7} \times 800 \times 1500 \approx 1.51 T$
(iii) · 1 mark
Find the magnetisation of the core.
Answer
Answer: About $1.2 \times 1 0^{6} A m^{- 1}$
$M = (μ_{r} - 1) H = 799 \times 1500 \approx 1.2 \times 1 0^{6} A m^{- 1}$
(iv) · 1 mark
What type of material is the core?
Answer
Answer: Ferromagnetic
χ = 799 is very large and positive.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Draw the pattern of magnetic field lines when (a) a diamagnetic and (b) a paramagnetic substance is placed in a uniform magnetic field. [2 marks] (2 marks)

Step	Marks
(a) Lines bend away from the diamagnetic sample; fewer lines pass through it than through the same area outside	1
(b) Lines bend slightly towards and crowd into the paramagnetic sample	1

A solenoid having 1000 turns per metre carries 2 A and has a core of relative permeability 500. Find (a) H, (b) M, (c) B inside the core. [3 marks] (3 marks)

Step	Marks
(a) $H = n I = 1000 \times 2 = 2000 A m^{- 1}$	1
(b) $M = (μ_{r} - 1) H = 499 \times 2000 \approx 1.0 \times 1 0^{6} A m^{- 1}$	1
(c) $B = μ_{0} μ_{r} H = 4 π \times 1 0^{- 7} \times 500 \times 2000 \approx 1.26 T$	1

Distinguish between diamagnetic, paramagnetic and ferromagnetic substances on the basis of (a) susceptibility, (b) relative permeability, (c) behaviour in a non-uniform field, (d) atomic origin, (e) effect of temperature. Give one example of each. [5 marks] (5 marks)

Step	Marks
(a) χ: small negative / small positive / very large positive	1
(b) μr: slightly less than 1 / slightly more than 1 / much greater than 1	1
(c) Move to weaker field (repelled) / to stronger field (weakly attracted) / to stronger field (strongly attracted)	1
(d) No net permanent atomic moment (induced, opposite) / permanent moments randomly oriented / aligned moments in domains	1
(e) Little effect / magnetisation falls as T rises / becomes paramagnetic above a certain temperature; examples bismuth, aluminium, iron	1

Where students lose marks in Magnetism and Matter

The slips examiners see most often, and what to write instead.

Mistake: Calling copper paramagnetic
Confusing metals with magnetic metals.
Do this: Copper is diamagnetic. Learn two examples of each class by heart.
Usually costs: 1 mark in MCQs and assertion-reason.
Mistake: Drawing field lines of a bar magnet stopping at the poles
Copying electric field line habits.
Do this: Magnetic field lines are closed loops: draw them continuing inside the magnet from S to N.
Usually costs: ½-1 mark.
Mistake: Writing $B = μ_{0} H$ inside a material with a core
Forgetting magnetisation.
Wrong working
Core $μ_{r} = 600$ : $B = 4 π \times 1 0^{- 7} \times 1500$
Right working
$B = μ_{0} μ_{r} H = 600 \times 4 π \times 1 0^{- 7} \times 1500 \approx 1.13 T$
Do this: Inside matter, multiply by $μ_{r}$ (or add M).
Usually costs: 1-2 marks.
Mistake: Saying diamagnetic materials have permanent atomic moments
Mixing up the causes.
Do this: Diamagnetic atoms have no net permanent moment (it is induced, opposite to B); paramagnetic atoms have permanent moments; ferromagnets have domains.
Usually costs: 1 mark in reasoning items.
Mistake: Writing long derivations for the bar magnet as a solenoid
Older books include them.
Do this: These are qualitative only for 2026-27: explain with the iron-filings pattern and the current-loop idea.
Usually costs: Time.

NCERT exercise guide: Magnetism and Matter

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Exercises 5.1, 5.2 and 5.5 (magnet in a uniform field)

What it tests: Torque on a magnet at an angle, the magnet's moment from the torque, stable and unstable positions, and the work to turn a magnet.

How to approach it: $τ = m B sin θ$ and $U = - m B cos θ$ ; work = $U_{f ina l} - U_{ini t ia l}$ .

Same kind as Exercises 5.2 and 5.5

A magnet of moment $0.5 J T^{- 1}$ is in a uniform field of 0.2 T. Find its potential energy in the stable and unstable positions, and the work needed to turn it from the stable to the unstable position.

Show the solutionSolution

Stable (θ = 0): $U = - m B = - 0.1 J$
Unstable (θ = 180°): $U = + m B = + 0.1 J$
Work $= 0.1 - (- 0.1) = 0.2 J$

Answer: −0.1 J, +0.1 J; 0.2 J

Exercises 5.3, 5.4 and 5.6 (solenoid as a magnet)

What it tests: Magnetic moment of a current-carrying solenoid, the torque on it in a field, and how it behaves when free to turn.

How to approach it: $m = N I A$ ; then $τ = m B sin θ$ ; a free solenoid turns until $m$ lies along $B$ .

Same kind as Exercise 5.3

A closely wound solenoid of 500 turns and cross-section $2 \times 1 0^{- 4} m^{2}$ carries 4 A. Find its magnetic moment and the torque on it when its axis is at $3 0^{\circ}$ to a field of 0.5 T.

Show the solutionSolution

$m = N I A = 500 \times 4 \times 2 \times 1 0^{- 4} = 0.4 A m^{2}$
$τ = m B sin 3 0^{\circ} = 0.4 \times 0.5 \times 0.5 = 0.1 N m$

Answer: $0.4 A m^{2}$ ; 0.1 N m

Exercise 5.7 (field on the axis and equator of a short magnet)

What it tests: Field of a short bar magnet at given distances on its axis and its equatorial line.

How to approach it: Axial $\frac{μ _{0}}{4 π} \frac{2 m}{r ^{3}}$ , equatorial $\frac{μ _{0}}{4 π} \frac{m}{r ^{3}}$ .

Same kind as Exercise 5.7

A short magnet of moment $0.25 J T^{- 1}$ . Find the field at 5 cm from its centre on (a) its axis, (b) its equatorial line.

Show the solutionSolution

$r^{3} = (0.05)^{3} = 1.25 \times 1 0^{- 4} m^{3}$
(a) $B = 1 0^{- 7} \times \frac{0.5}{1.25 \times 1 0 ^{- 4}} = 4 \times 1 0^{- 4} T$
(b) $B = 1 0^{- 7} \times \frac{0.25}{1.25 \times 1 0 ^{- 4}} = 2 \times 1 0^{- 4} T$

Answer: (a) $4 \times 1 0^{- 4} T$ along the axis (b) $2 \times 1 0^{- 4} T$ , opposite to $m$

Magnetism and Matter: previous year questions

Asked in 4 of the 8 board papers we hold (2023 to 2026), on average 0.6 marks per paper; 5 questions in all, counting OR alternatives. In 3 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Magnetism and Matter

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

2026, set 55/1/1, Q13 · 1 mark · Assertion-reasonCompetency-based

Assertion (A) : All atoms have a net magnetic moment.
Reason (R) : A current loop does not always behave as a magnetic dipole.

(A)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
(B)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
(C)Assertion (A) is true, but Reason (R) is false.
(D)Both Assertion (A) and Reason (R) are false.

Try it first, then show our solutionSolution

The assertion is false: atoms of diamagnetic substances have zero net magnetic moment.
The reason is false: a current loop always behaves as a magnetic dipole with moment $m = I A$ . Both are false.
1 mark

Answer: Option (D)

Where the marks are

Identifies both A and R as false (1 mark)

See it in the full 2026 board paper, set 55/1/1

Every Magnetism and Matter question, by year

For 2027

Sample paper 2026-27: Q8 (1 mark, solved), Q20(A) (2 marks, solved), Q20(B) (2 marks, solved)

2026

Set 55/1/1: Q13 (1 mark, solved)

Sample paper 2025-26: Q12 (1 mark, solved), Q20(II) (2 marks, solved), Q27(II) (3 marks, solved)

2024

Set 55/5/1: Q3 (1 mark, solved)

Sample paper 2023-24: Q6 (1 mark, solved)

2023

Set 55/1/1: Q5 (1 mark, solved), Q16 (1 mark, solved)

Set 55/5/1: Q3 (1 mark, solved)

Practice questions on Magnetism and Matter

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which of these is ferromagnetic?
(a) aluminium
(b) copper
(c) nickel
(d) sodium
Hint
Fe, Co, Ni, Gd.
Answer
(c) nickel
Q2 · 1 mark · MCQBoard level
The SI unit of magnetisation is:
(a) T
(b) A m⁻¹
(c) A m²
(d) Wb
Hint
Magnetic moment per unit volume.
Answer
(b) A m⁻¹
Q3 · 1 mark · Very short answerBoard level
State the sign of the magnetic susceptibility of a diamagnetic and of a paramagnetic substance.
Hint
Opposes or supports the field?
Answer
Diamagnetic: small negative. Paramagnetic: small positive.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The field lines of a bar magnet form closed loops.
Reason (R): Isolated magnetic poles do not exist.
(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.
Hint
Where could a line start or end?
Answer
(a)
Q5 · 2 marks · Very short answerHarder board level
A material has relative permeability 0.99998. Find its susceptibility, classify it, and give one example of such a material.
Hint
χ = μr − 1.
Answer
$χ = - 2 \times 1 0^{- 5}$ ; diamagnetic; e.g. bismuth, copper or water.
Q6 · 2 marks · Very short answerHarder board level
A bar magnet of moment $0.6 J T^{- 1}$ is placed in a uniform field of 0.05 T. (a) Find the torque on it when its moment makes $3 0^{\circ}$ and when it makes $15 0^{\circ}$ with the field. (b) In each case, which way does it tend to turn? (c) In which two orientations is the torque zero, and which of them is stable?
Hint
$τ = m B sin θ$ , and $sin 3 0^{\circ} = sin 15 0^{\circ}$ .
Answer
(a) $τ = 0.6 \times 0.05 \times 0.5 = 0.015 N m$ in both cases. (b) In each case the torque turns $m$ towards $B$ : at $3 0^{\circ}$ it swings back to $0^{\circ}$ ; at $15 0^{\circ}$ it swings away from $18 0^{\circ}$ towards $0^{\circ}$ . (c) Zero torque at $0^{\circ}$ (stable: a small push brings it back) and $18 0^{\circ}$ (unstable: a small push turns it right round).
Q7 · 3 marks · Short answerHarder board level
A solenoid of 1000 turns per metre carries 0.7 A. With an iron core inside, the field measured in the core is 0.88 T. Find H, the relative permeability of the core, its susceptibility and its magnetisation. ( $μ_{0} = 4 π \times 1 0^{- 7} T m A^{- 1}$ )
Hint
Find H first, then $μ_{r} = \frac{B}{μ _{0} H}$ .
Answer
$H = n I = 700 A m^{- 1}$ ; $μ_{r} = \frac{0.88}{4 π \times 1 0 ^{- 7} \times 700} = \frac{0.88}{8.8 \times 1 0 ^{- 4}} \approx 1000$ ; $χ = μ_{r} - 1 \approx 999$ ; $M = χH \approx 999 \times 700 \approx 7.0 \times 1 0^{5} A m^{- 1}$ .
Q8 · 1 mark · Very short answerHarder board level
The axial field of a short magnet at distance r is B. What is the field (a) on the axis at 2r, (b) on the equatorial line at r?
Hint
$B \propto 1/ r^{3}$ ; equatorial is half of axial.
Answer
(a) B/8 (b) B/2
Q9 · 2 marks · Very short answerHarder board level
A coil of 10 turns, each of area $0.02 m^{2}$ , carries 5 A. Treating it as a magnetic dipole, find its moment and its field on the axis 20 cm away (far-field form).
Hint
m = NIA.
Answer
$m = 10 \times 5 \times 0.02 = 1 A m^{2}$ ; $B = 1 0^{- 7} \times \frac{2 \times 1}{( 0.2 ) ^{3}} = 1 0^{- 7} \times 250 = 2.5 \times 1 0^{- 5} T$ .
Q10 · 2 marks · Very short answerHOTS / competency
A paramagnetic sample is cooled from room temperature to a much lower temperature in the same applied field. Will its magnetisation increase or decrease? Would a diamagnetic sample behave in the same way? Explain.
Hint
Which of them has permanent moments that heat disturbs?
Answer
The paramagnet's magnetisation increases, because lower thermal agitation lets more permanent atomic moments stay aligned. A diamagnet's induced moment does not depend on aligning permanent moments, so it changes very little with temperature.
Q11 · 2 marks · Very short answerHOTS / competency
Two small watch glasses containing a paramagnetic liquid are placed on the poles of a magnet: once with the poles close together and once far apart. Describe the shape of the liquid surface in each case. What would a diamagnetic liquid do?
Hint
Where is the field strongest in each arrangement?
Answer
Poles close: the field is strongest in the middle, so the paramagnetic liquid collects there (a hump in the middle). Poles far apart: the field is strongest near the poles, so the liquid moves towards the edges (a dip in the middle). A diamagnetic liquid does the opposite in each case.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Why do magnetic field lines form closed loops?Show answer
Because there are no magnetic monopoles; lines run N to S outside and S to N inside the magnet.
2.Write the relation between B, H and M.Show answer
$B = μ_{0} (H + M)$ .
3.Define magnetic susceptibility.Show answer
$χ = M / H$ , the ratio of magnetisation to magnetic intensity; it measures how strongly a material responds to a field.
4.Give the signs of χ for dia-, para- and ferromagnetic materials.Show answer
Small negative; small positive; large positive.
5.Name two diamagnetic, two paramagnetic and two ferromagnetic materials.Show answer
Bismuth, copper; aluminium, sodium; iron, nickel.
6.What is χ for a superconductor?Show answer
−1 (perfect diamagnet; μr = 0).
7.How does the magnetisation of a paramagnet change with temperature, and why?Show answer
It decreases as temperature rises, because thermal agitation disturbs the alignment of atomic moments.
8.A solenoid of 1000 turns per metre carries 2 A. Find H.Show answer
$H = n I = 2000 A m^{- 1}$ .

Best order to study it

Start with the bar magnet, its poles and its field lines; compare with electric field lines.
Learn the bar magnet as an equivalent solenoid, with its axial and equatorial fields, qualitatively.
Learn the torque and energy of a magnetic dipole in a uniform field, again qualitatively, using the electric dipole analogy.
Study magnetisation, magnetic intensity, susceptibility and permeability, with one solenoid-core numerical.
Learn diamagnetism, paramagnetism and ferromagnetism: cause, sign of χ, behaviour, examples and field-line pictures.
Finish with the effect of temperature on each kind of material.

Quick revision checklist

The night before the exam: can you do each of these without looking?

Can you explain why cutting a magnet never gives a single pole?
Can you draw the field lines of a bar magnet, inside and outside?
Can you state, qualitatively, how the axial and equatorial fields of a short magnet compare?
Can you say which orientation of a magnet in a field is stable and which unstable?
Can you write $B = μ_{0} (H + M)$ , $M = χH$ and $μ_{r} = 1 + χ$ ?
Can you find H, B and M for a solenoid with a core?
Can you classify a material from χ or μr?
Can you draw field lines for dia- and paramagnetic samples in a uniform field?
Can you name two examples of each kind of material?
Can you explain the effect of temperature on para- and ferromagnetism?

Magnetism and Matter: frequently asked questions

Is Earth's magnetism in the 2026-27 syllabus?

No. Earth's magnetism, magnetic declination and dip are not in the 2026-27 syllabus.

Are Curie's law and hysteresis asked?

No. Curie's law, the Curie temperature in detail and hysteresis are not in the 2026-27 syllabus. You should still know qualitatively that heating weakens paramagnetism and that a ferromagnet becomes paramagnetic when heated enough.

Do I need to derive the field of a bar magnet?

No. The bar magnet as an equivalent solenoid, its axial and equatorial fields, and the torque on it are listed as 'qualitative treatment only'. Know the results and the dipole analogy.

Is Gauss's law for magnetism in the syllabus?

NCERT section 5.3 is not named in the CBSE content list. However, the 2026-27 sample paper asked for its statement and significance, so learn the one line: the net magnetic flux through any closed surface is zero, because magnetic monopoles do not exist.

Why are superconductors called perfect diamagnets?

They expel a magnetic field completely from their interior (χ = −1, μr = 0), the extreme case of the diamagnetic behaviour of opposing an applied field.

How many marks does this chapter carry?

It is part of Units III and IV together, which carry 17 of the 70 marks along with Moving Charges and Magnetism, Electromagnetic Induction and Alternating Current. Questions from this chapter are usually 1 or 2 marks.

Based on: CBSE Physics (042) syllabus 2026-27; NCERT Physics Part I, Textbook for Class XII, Chapter 5 (Reprint 2026-27)