Previous year questions: Magnetism and Matter

The questions below come from official CBSE board papers and official Sample Question Papers. The year label in each heading is printed on the source, and the marks are the marks printed for that question or part. Try the question before reading the answer.

Q1 (CBSE Board 2023, 1 mark)

A diamagnetic substance is brought near the north or south pole of a bar magnet. It will be (a) repelled by both the poles (b) attracted by both the poles (c) attracted by the north pole and repelled by the south pole (d) attracted by the south pole and repelled by the north pole

Answer: Option (a), repelled by both poles. A diamagnetic material has a small negative susceptibility, so the induced magnetic moment points opposite to the external field. The material is therefore weakly repelled no matter which pole is brought near it, and it moves from the stronger field region towards the weaker one.

Q2 (CBSE Board 2023, 1 mark)

Assertion (A): If copper is put in a magnetic field, the flux lines inside it end up more crowded than those in the air around it. Reason (R): Copper is a paramagnetic material.

Answer: Both statements are false, so the answer is option (D). Copper is a diamagnetic material, not paramagnetic, and a diamagnetic material weakly expels field lines instead of drawing them in. So the field lines inside copper are slightly less dense than outside, and both statements fail.

Q3 (CBSE Board 2025, 1 mark)

A bar magnet is initially at right angles to a uniform magnetic field. The magnet is rotated till the torque acting on it becomes one half of its initial value. The angle through which the bar magnet is rotated is (A) 30 degrees (B) 45 degrees (C) 60 degrees (D) 75 degrees

Answer: Option (C), 60 degrees. The torque is tau = mB sin theta. At right angles the torque is mB, so the new torque is mB/2, which needs sin theta = 1/2. That gives theta equal to 30 degrees or 150 degrees. Turning from 90 degrees to either of these needs a rotation of 60 degrees, so the answer is option (C). Note that the direction of rotation is not fixed by the data: turning towards 30 degrees or towards 150 degrees both change the angle by 60 degrees, which is why the option list gives a single value.

Q4 (CBSE Board 2025, 1 mark)

Which one of the following materials is not paramagnetic? (A) Aluminium (B) Sodium chloride (C) Calcium (D) Copper chloride

Answer: Option (B), sodium chloride. Aluminium has unpaired electrons and is paramagnetic, with a small positive susceptibility, and calcium is also paramagnetic for the same reason. In sodium chloride the sodium and chloride ions both have closed electron shells, so there are no permanent atomic moments and the material is diamagnetic. Copper chloride is a salt of a transition metal ion and shows paramagnetic behaviour from its unpaired d electrons, so it is not the answer either.

Q5 (CBSE Board 2025, 1 mark)

The materials having negative magnetic susceptibility are (A) diamagnetic (B) paramagnetic (C) ferromagnetic (D) all of these

Answer: Option (A), diamagnetic. Susceptibility chi = M/H is negative when the induced magnetisation opposes the applied field. Diamagnets show exactly this behaviour, with chi of the order of minus one in a million, while paramagnets and ferromagnets have positive susceptibility.

Q6 (CBSE Board 2026, 1 mark)

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

Answer: Both statements are false, so the answer is option (D). An atom has a net magnetic moment only when its electron spins and orbital motions do not cancel, so atoms with completely paired electrons have zero net moment and the assertion fails. A current loop has a magnetic moment m = IA and behaves as a dipole at distances large compared with the loop, so the reason fails as well. Judge the assertion and the reason independently before choosing the option.

Q7 (CBSE SQP 2023-24, 1 mark)

The relative magnetic permeability of a substance X is slightly less than unity and that of a substance Y is slightly more than unity. Then (a) X is paramagnetic and Y is ferromagnetic (b) X is diamagnetic and Y is ferromagnetic (c) X and Y both are paramagnetic (d) X is diamagnetic and Y is paramagnetic

Answer: Option (d). Relative permeability is mur = 1 + chi. A value just below one means a small negative chi, which is diamagnetic. A value just above one means a small positive chi, which is paramagnetic. A ferromagnetic material would have a permeability of the order of a thousand, not slightly more than one. The option pair (d) is therefore the only one that fits both observations, and the question is testing the sign of chi rather than any numerical value.

Q8 (CBSE SQP 2023-24, 1 mark)

An electron with angular momentum L moving around the nucleus has a magnetic moment given by (a) eL/2m (b) eL/3m (c) eL/4m (d) eL/m

Answer: Option (a), eL/2m. An electron in a circular orbit is a current loop, and working out the magnetic moment of the loop gives the ratio of magnetic moment to angular momentum as e/2m, a result called the gyromagnetic ratio. The same ratio appears in the Bohr model, where one unit of orbital angular momentum gives one Bohr magneton.

Q9 (CBSE SQP 2025-26, 2 marks)

Draw a diagram representing the behaviour of magnetic field lines for a (A) diamagnetic substance and (B) paramagnetic substance.

Answer: For a diamagnet the field lines are slightly expelled from the material: the lines crowd together outside and become less dense inside the specimen, because the induced magnetisation opposes the field. For a paramagnet the lines are slightly concentrated inside the material, because its atomic moments align with the field and add to it. In both diagrams the lines remain closed and continuous, and the difference from the surrounding field is small, which matches the tiny magnitudes of diamagnetic and paramagnetic susceptibility.

Q10 (CBSE SQP 2025-26, 2 marks)

State Gauss's law of magnetism. Hence find the magnetic flux linked with a sphere enclosing a current carrying solenoid.

Answer: Gauss's law for magnetism says that the total magnetic flux passing out of any closed surface is zero. A sphere drawn around a current carrying solenoid is exactly such a closed surface, and because each field line is a closed loop, every line that goes into the sphere somewhere must come out somewhere else. The outward count therefore matches the inward count, so the net flux linked with the sphere is zero. The same argument works for the field of a bar magnet or of a current loop.

How marks are usually split

In a one mark assertion and reason question the marks come from judging A and R separately, so write whether each is true before giving the reason. For the material class questions, quote the sign and rough size of the susceptibility, because that single data item fixes the class and the behaviour. Numeric questions on the torque or energy of a dipole need the formula written first, then the substitution, then the unit.

For the field line diagrams, draw closed continuous lines, mark the direction with arrows, and show the difference from the surrounding field clearly: expelled lines for a diamagnet, slightly concentrated lines for a paramagnet. For Gauss's law questions, write the law in words and then use the closed loop property of field lines to argue that the net flux through any closed surface is zero, which is the answer even when the surface encloses a solenoid.

The exercise style questions in this chapter are short: a torque or a magnetic moment is usually one substitution, and an earth's field question is one resolution into components. Write the data, the formula and the answer with its unit in three lines, and do not spend more than two minutes on a one mark item.