Class 12 Physics Chapter 5 Important Questions (2026-27)

Class 12 Physics Chapter 5 Magnetism and Matter: important questions with answers on the bar magnet and Earth's magnetism for CBSE 2026-27.

Important Questions for Class 12 Physics Chapter 5 – Magnetism and Matter

Looking for Class 12 Physics Chapter 5 important questions? This page covers Magnetism and Matter with exam-focused questions and step-by-step answers, arranged by marks: 1 mark, 2–3 marks and 5 marks. Written for the CBSE 2026–27 syllabus, it focuses on the bar magnet, magnetic field lines and Earth's magnetism. Attempt them after finishing the NCERT chapter.

Very Short Answer Questions (1 Mark)

Classification of Magnetic Materials

Question 1

The permeability of a magnetic material is 0.9983. Name the type of magnetic material it represents.

Answer: It represents diamagnetic material (since \(\mu_r < 1\)).

Question 2

The susceptibility of a magnetic material is \(1.9 \times 10^{-5}\). Name the type of magnetic material it represents.

Answer: It represents a paramagnetic substance (small positive susceptibility).

Question 3

The susceptibility of a magnetic material is \(-4.2 \times 10^{-6}\). Name the type of magnetic material it represents.

Answer: It represents a diamagnetic substance (negative susceptibility).

Question 4

Relative permeability of a material, \(\mu_r = 0.5\). Identify the nature of the magnetic material and write its relation to magnetic susceptibility.

Answer: It is a diamagnetic material. The relation is \(\mu_r = 1 + \chi_m\).

Question 5

Relative permeability of a material \(\mu_r = 400\). Identify the nature of the magnetic material.

Answer: It is ferromagnetic (very large permeability).

Question 6

Relative permeability (\(\mu_r\)) of a material has a value lying \(1 < \mu_r < 1 + \varepsilon\) (where \(\varepsilon\) is a small quantity). Identify the nature of the magnetic material.

Answer: The substance is paramagnetic.

Question 7

Which of the following substances are diamagnetic: Bi, Al, Na, Cu, Ca and Ni?

Answer: Bi and Cu are diamagnetic.

Question 8

Which of the following substances are paramagnetic: Bi, Al, Cu, Ca, Pb, Ni?

Answer: Al and Ca are paramagnetic.

Earth's Magnetism

Question 9

Where on the surface of Earth is the angle of dip \(90^\circ\)?

Answer: At the magnetic poles, the angle of dip is \(90^\circ\).

Question 10

Where on the surface of Earth is the angle of dip zero?

Answer: At the magnetic equator, the angle of dip is \(0^\circ\).

Question 11

Where on the surface of Earth is the vertical component of Earth's magnetic field zero?

Answer: At the magnetic equator, the vertical component of Earth's magnetic field is zero.

Question 12

Where on the surface of Earth is the horizontal component of Earth's magnetic field zero?

Answer: At the poles of Earth, the horizontal component is zero.

Question 13

Where on the surface of Earth is Earth's magnetic field perpendicular to the surface?

Answer: At the poles of the Earth.

Question 14

The horizontal component of Earth's magnetic field at a place is B and angle of dip is \(60^\circ\). What is the value of the vertical component of Earth's magnetic field at the equator?

Answer: At the equator, the angle of dip is \(0^\circ\), so the vertical component \(B_V = B_H \tan\delta = B \times \tan 0^\circ = 0\).

Question 15

At a place, the horizontal component of Earth's magnetic field is B and the angle of dip is \(60^\circ\). What is the value of the horizontal component of Earth's magnetic field at the equator?

Answer: \(B_H = B\cos\delta\). So the total field \(B_E = \dfrac{B}{\cos 60^\circ} = 2B\). At the equator, \(\delta = 0^\circ\), so the horizontal component equals the total field: 2B.

Magnets and Magnetic Field Sources

Question 16

Current flows through a circular loop. Depict the north and south poles of its equivalent magnetic dipole.

Answer: The face of the loop from which the current appears anticlockwise acts as the north pole; the face from which it appears clockwise acts as the south pole (right-hand thumb rule).

Question 17

A straight wire extending from east to west falls with a speed v at right angles to the horizontal component of the Earth's magnetic field. Which end of the wire would be at higher electrical potential and why?

Answer: The west end is at higher potential, because by Fleming's right-hand rule the induced emf is directed from west to east.

Question 18

What are permanent magnets? Give one example.

Answer: Substances which at room temperature retain their ferromagnetic property for a long period of time are called permanent magnets. Example: steel, alnico.

Question 19

Is the steady electric current the only source of magnetic field? Justify your answer.

Answer: No. Steady current is not the only source of magnetic field. Magnets are also sources of magnetic field, and unsteady current also produces a varying magnetic field.

Question 20

The motion of a copper plate is damped when it is allowed to oscillate between the two poles of a magnet. What is the cause of this damping?

Answer: The cause of this damping is the eddy current induced in the copper plate.

Short Answer Questions (2–3 Marks)

Magnetic Susceptibility and Material Behaviour

Question 21

In what way is the behaviour of a diamagnetic material different from that of a paramagnetic when kept in an external magnetic field?

Answer:
  • A diamagnetic specimen moves towards the weaker region of the field; a paramagnetic specimen moves towards the stronger region.
  • A diamagnetic specimen is repelled by a magnet; a paramagnetic specimen is attracted towards the magnet.
  • A paramagnetic specimen aligns along the field, while a diamagnetic specimen aligns perpendicular to it.

Question 22

Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

Answer: Magnetic susceptibility \(\chi_m\) is the property of a material which determines how easily it can be magnetised when kept in a magnetising field. It is the ratio of the intensity of magnetisation \(I\) produced to the intensity of magnetising field \(H\): \(\chi_m = \dfrac{I}{H}\).

Positive susceptibility: paramagnetic material, e.g. Al, Ca.
Negative susceptibility: diamagnetic material, e.g. Bi, Cu.

Negative susceptibility signifies that the material is diamagnetic in nature.

Question 23

The figure shows the variation of intensity of magnetisation versus the applied magnetic field intensity \(H\) for two magnetic materials A and B. (a) Identify the materials A and B. (b) Why does material B have a larger susceptibility than A for a given field at constant temperature?

Answer: (a) Material B has a higher positive slope (higher susceptibility) → ferromagnetic. Material A has a lower positive slope → paramagnetic.

(b) The larger susceptibility of B is due to its characteristic domain structure — a larger number of magnetic moments align in the direction of the magnetising field compared to paramagnetic materials for the same value of magnetising field.

Question 24

The susceptibility of a magnetic material is \(-2.6 \times 10^{-5}\). Identify the type of magnetic material and state its two properties.

Answer: The material is diamagnetic (negative susceptibility). Properties:
  • In a non-uniform field, it moves from stronger to weaker parts of the field.
  • A freely suspended diamagnetic rod aligns itself perpendicular to the field.
  • It expels magnetic field lines and is repelled by a magnet.

Question 25

The susceptibility of a magnetic material is \(2.6 \times 10^{-5}\). Identify the type of magnetic material and state its two properties.

Answer: The material is paramagnetic. Properties:
  • It is feebly attracted by magnets.
  • In a non-uniform field, it moves from weaker to stronger parts of the field.

Question 26

The relative magnetic permeability of a magnetic material is 800. Identify the nature of the magnetic material and state its two properties.

Answer: The substance is ferromagnetic. Properties:
  • It is strongly attracted by magnets.
  • In a non-uniform field, it moves quickly from weaker to stronger parts of the field.

Question 27

Out of the two magnetic materials, 'A' has relative permeability slightly greater than unity while 'B' has less than unity. Identify the nature of the materials 'A' and 'B'. Will their susceptibilities be positive or negative?

Answer: 'A' is paramagnetic (\(\mu_r > 1\)), 'B' is diamagnetic (\(\mu_r < 1\)).

The susceptibility of A is positive; of B is negative.

Question 28

State two characteristic properties distinguishing the behaviour of paramagnetic and diamagnetic materials.

Answer:
Paramagnetic Diamagnetic
Susceptibility is small and positive (\(0 < \chi_m < \varepsilon\)).Susceptibility is small and negative (\(-1 \le \chi_m < 0\)).
Feebly attracted by magnets.Feebly repelled by magnets.

Question 29

State two characteristic properties distinguishing the behaviour of diamagnetic and ferromagnetic materials.

Answer:
Diamagnetic Ferromagnetic
Relative permeability \(\mu_r < 1\).Relative permeability very large (\(\mu_r \approx 10^3\) to \(10^5\)).
Susceptibility has a small negative value (\(-1 \le \chi_m \le 0\)).Susceptibility is very large (\(\chi_m \gg 1\)).

Question 30

(a) How does a diamagnetic material behave when it is cooled to very low temperatures? (b) Why does a paramagnetic sample display greater magnetisation when cooled? Explain.

Answer: (a) At very low temperatures, a diamagnetic material exhibits perfect conductivity and perfect diamagnetism (Meissner effect).

(b) At lower temperatures, the random thermal motion that disrupts dipole alignment is reduced, so the tendency for dipoles to align with the field increases, giving greater magnetisation.

Magnetic Field Lines in Materials

Question 31

Draw magnetic field lines when a (i) diamagnetic (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances?

Answer: (i) For a diamagnetic material, the field lines become slightly less dense inside the material (expelled). (ii) For a paramagnetic material, the field lines become slightly more dense inside (concentrated).

Magnetic susceptibility distinguishes this behaviour — negative for diamagnetic and small positive for paramagnetic.

Question 32

Depict the behaviour of magnetic field lines when (i) a diamagnetic material and (ii) a paramagnetic material is placed in an external magnetic field. Mention briefly the properties of these materials which explain this distinguishing behaviour.

Answer: Diamagnetic: Field lines are expelled (less dense inside). Property: a rod of diamagnetic material suspended in a magnetic field sets itself at right angles to the field; the material has negative susceptibility.

Paramagnetic: Field lines are concentrated (more dense inside). Property: a rod of paramagnetic material suspended in a magnetic field sets itself parallel to the field; the material has small positive susceptibility.

Question 33

Show diagrammatically the behaviour of magnetic field lines in the presence of (i) paramagnetic and (ii) diamagnetic substances. How does one explain this distinguishing feature?

Answer: (i) Paramagnetic: field lines become more concentrated inside. (ii) Diamagnetic: field lines become less concentrated inside.

Explanation: The relative permeability of a paramagnetic substance is \(\mu_r > 1\) and of a diamagnetic substance is \(\mu_r < 1\).

Question 34

Depict the behaviour of magnetic field lines near (i) diamagnetic and (ii) paramagnetic substances. Justify, giving reasons.

Answer: (i) Diamagnetic: field lines are expelled and the field inside is reduced.

(ii) Paramagnetic: individual atomic dipoles align with the applied field, so field lines get concentrated inside and the field is enhanced.

Permanent Magnets and Electromagnets

Question 35

(i) Write two characteristics of a material used for making permanent magnets. (ii) Why is the core of an electromagnet made of ferromagnetic materials?

Answer: (i) Two characteristics for permanent magnets: (a) high retentivity (to produce a strong field), (b) high coercivity (so magnetisation is not destroyed by stray fields, temperature or mechanical damage).

(ii) The core of an electromagnet is made of ferromagnetic materials because they have high initial permeability (large magnetisation for small field) and low resistivity (to reduce eddy current losses).

Question 36

Write two characteristic properties each to select materials suitable for (i) permanent magnets and (ii) electromagnets.

Answer: (a) Permanent magnet: High retentivity, high coercivity, high permeability (any two).

(b) Electromagnet: High permeability, low retentivity, low coercivity (any two).

Question 37

Write two properties of a material suitable for making (a) a permanent magnet, and (b) an electromagnet.

Answer: Same as Question 36.

Question 38

(a) How is an electromagnet different from a permanent magnet? (b) Write two properties of a material which make it suitable for making electromagnets.

Answer: (a) A permanent magnet retains its magnetic properties for a long time at room temperature. An electromagnet consists of a ferromagnetic core inside a solenoid and behaves like a magnet only while current flows.

(b) Properties for electromagnets: high permeability, low retentivity, low coercivity.

Magnetic Moment of Coils

Question 39

A circular coil of N turns and radius R carries a current I. It is unwound and rewound to make another coil of radius R/2, the current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and the original coil.

Answer: Total length of wire \(= 2\pi R N\). For the new coil of radius \(R/2\), number of turns \(N' = \dfrac{2\pi R N}{2\pi (R/2)} = 2N\).

Magnetic moment \(M = NIA\). Original: \(M_1 = NI\pi R^2\). New: \(M_2 = (2N)I\pi (R/2)^2 = \dfrac{NI\pi R^2}{2}\).

Ratio \(M_2 : M_1 =\) 1 : 2.

Question 40

A circular coil of N turns and diameter d carries a current I. It is unwound and rewound to make another coil of diameter 2d, the current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and the original coil.

Answer: New turns \(N' = \dfrac{N}{2}\). Original moment \(M_1 = NI\pi (d/2)^2\). New moment \(M_2 = \dfrac{N}{2} I \pi d^2 = \dfrac{N}{2} I \pi (2 \cdot d/2)^2 = \dfrac{N}{2} I \times 4\pi (d/2)^2 = 2NI\pi (d/2)^2 = 2M_1\).

Ratio \(M_2 : M_1 =\) 2 : 1.

Question 41

A coil of N turns and radius R carries a current I. It is unwound and rewound to make a square coil of side a having the same number of turns N. Keeping the current I the same, find the ratio of the magnetic moments of the square coil and the circular coil.

Answer: Same length of wire: \(2\pi R N = 4aN \Rightarrow a = \dfrac{\pi R}{2}\).

\(M_{circ} = NI\pi R^2\), \(M_{sq} = NI a^2 = NI\dfrac{\pi^2 R^2}{4}\).

Ratio \(M_{sq} : M_{circ} = \dfrac{\pi^2}{4} : \pi =\) \(\pi : 4\).

Earth's Magnetic Field Calculations

Question 42

A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its north tip down at \(60^\circ\) with the horizontal. The horizontal component of Earth's magnetic field at the place is 0.4 G. Determine the magnitude of Earth's magnetic field at the place.

Answer: \(B_H = B\cos\delta \Rightarrow B = \dfrac{B_H}{\cos 60^\circ} = \dfrac{0.4}{0.5} =\) 0.8 G.

Question 43

Define the following using suitable diagrams: (i) magnetic declination and (ii) angle of dip. In what direction will a compass needle point when kept at the (i) poles and (ii) equator?

Answer: (i) Magnetic declination: the angle between the magnetic meridian and the geographical meridian at a place.

(ii) Angle of dip: the angle which the magnetic needle makes with the horizontal in the magnetic meridian.

Compass needle direction: (i) at the poles — vertical to the Earth's surface; (ii) at the equator — parallel to the Earth's surface.

Long Answer Questions (5 Marks)

Question 44

(a) A small compass needle of magnetic moment m is free to turn about an axis perpendicular to the direction of a uniform magnetic field B. The moment of inertia of the needle about the axis is I. The needle is slightly disturbed from its stable position and then released. Prove that it executes simple harmonic motion. Hence deduce the expression for its time period. (b) A compass needle, free to turn in a vertical plane, orients itself with its axis vertical at a certain place on the Earth. Find out the values of (i) horizontal component of Earth's magnetic field and (ii) angle of dip at the place.

Answer: (a) When the needle is deflected by a small angle \(\theta\) from equilibrium, the torque is \(\tau = -mB\sin\theta \approx -mB\theta\) (for small \(\theta\)).

Using \(\tau = I\alpha = I\dfrac{d^2\theta}{dt^2}\): \(I\dfrac{d^2\theta}{dt^2} = -mB\theta\), so \(\dfrac{d^2\theta}{dt^2} = -\dfrac{mB}{I}\theta\). This is the SHM equation with \(\omega^2 = \dfrac{mB}{I}\).

Time period: \(T = 2\pi\sqrt{\dfrac{I}{mB}}\)

(b) Since the compass needle orients vertically: (i) horizontal component of Earth's magnetic field \(= 0\), (ii) angle of dip \(= 90^\circ\).

Key Formulas to Remember

Concept Formula
Magnetic susceptibility\(\chi_m = \dfrac{I}{H}\)
Relative permeability\(\mu_r = 1 + \chi_m\)
Magnetic moment of coil\(M = NIA\)
Torque on magnetic dipole\(\tau = mB\sin\theta\)
Horizontal component of Earth's field\(B_H = B\cos\delta\)
Vertical component of Earth's field\(B_V = B\sin\delta = B_H\tan\delta\)
Total Earth's field\(B = \sqrt{B_H^2 + B_V^2}\)
Time period of magnetic needle\(T = 2\pi\sqrt{\dfrac{I}{mB}}\)

FAQs

Are these questions enough for CBSE Class 12 Physics Chapter 5?

Yes. These questions cover every major topic — classification of magnetic materials, earth's magnetism (dip, declination, horizontal and vertical components), behaviour of diamagnetic, paramagnetic and ferromagnetic substances, permanent magnets and electromagnets — that CBSE has asked in previous board exams. Combine them with NCERT exercises and you'll be well prepared.

Which topics are most important for board exams?

Classification and properties of magnetic materials, magnetic susceptibility and relative permeability, behaviour of field lines in magnetic materials, earth's magnetic elements (declination, dip, horizontal and vertical components), properties needed for permanent magnets and electromagnets are consistently high-weightage topics.

How should I prepare for numericals in this chapter?

Practise problems on magnetic moment of coils (with changed shape or size), horizontal and vertical component calculations using \(B_H = B\cos\delta\) and \(B_V = B\sin\delta\), time period of a magnetic needle in a magnetic field, and problems involving relative permeability and susceptibility. Focus on understanding the conditions at the magnetic poles and equator.