Chapter 5: Magnetism and Matter Assertion-Reason Questions | physics Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): The net magnetic flux through any closed surface is always zero. Reason (R): Magnetic monopoles do not exist, so there are no sources or sinks of magnetic field B.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): A bar magnet placed in a uniform magnetic field experiences zero net force. Reason (R): In a uniform field, the forces on the north and south poles of the bar magnet are equal in magnitude and opposite in direction, cancelling each other.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): Magnetic field lines always form continuous closed loops. Reason (R): Magnetic field lines begin from the north pole and end at the south pole of a magnet.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): When a bar magnet is cut into two halves, we get two isolated magnetic poles — one north and one south. Reason (R): Magnetic monopoles do not exist in nature; isolated north or south poles cannot be created.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 5

Logic Check

Assertion (A): A superconductor is a perfect diamagnet. Reason (R): For a superconductor, chi = -1 and mu_r = 0, so the external magnetic field is completely expelled from its interior.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Two magnetic field lines can intersect each other at a point of strong magnetic field. Reason (R): At a point of intersection, the direction of the net magnetic field would be ambiguous.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): The magnetic potential energy of a dipole is minimum when the dipole moment is parallel to the external field. Reason (R): Potential energy U = -m.B = -mB cos(theta) is minimum when theta = 0 degrees, giving U = -mB.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): The magnetic field lines inside a toroid form complete closed loops entirely within the toroid. Reason (R): Each field line loop inside the toroid encloses a region through which a current is passing.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): A diamagnetic substance moves from the stronger to the weaker region of an external magnetic field. Reason (R): Diamagnetic substances have a small positive magnetic susceptibility.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): Magnetic susceptibility chi of a paramagnetic material depends on temperature. Reason (R): Both chi and mu_r of a paramagnetic material depend on the material and on the sample temperature; lowering temperature increases susceptibility.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): Diamagnetism is present in all substances. Reason (R): The mechanism of diamagnetism (Lenz's law effect on orbital electrons) operates in every atom that has orbiting electrons.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): A bar magnet and a current-carrying solenoid produce similar magnetic field patterns. Reason (R): The axial field of a finite solenoid at large distances has the same mathematical form as the axial field of a bar magnet.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 13

Logic Check

Assertion (A): A magnetic needle placed in a uniform field experiences zero net force. Reason (R): Magnetic force on a moving charge is always perpendicular to the velocity, so no net translational force acts on the needle.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): When a ferromagnet is heated above its Curie temperature, it becomes paramagnetic. Reason (R): Above the Curie temperature, thermal energy destroys the cooperative domain alignment, and individual atomic dipoles become randomly oriented.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): The magnetic field lines do not represent lines of force on a moving charged particle. Reason (R): The magnetic force on a moving charge (F = qv x B) is always perpendicular to B, not along the field line.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): Alnico is used for making permanent magnets. Reason (R): Alnico is a soft ferromagnetic material whose magnetisation disappears on removal of the external field.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 17

Logic Check

Assertion (A): A system can have a net magnetic moment even when its net electric charge is zero. Reason (R): Magnetic moments arise from circulating currents (moving charges), and the average of magnetic moments from various current loops may be non-zero even when net charge is zero.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): The equatorial field of a bar magnet at distance r is equal in magnitude to its axial field at the same distance. Reason (R): Both equatorial and axial fields of a short bar magnet are inversely proportional to r^3.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 19

Logic Check

Assertion (A): For a paramagnetic material, both chi and mu_r are greater than 1. Reason (R): For paramagnetic materials, chi is small and positive (0 < chi < epsilon), so mu_r = 1 + chi is slightly greater than 1.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): The magnetic field inside a ferromagnetic core of a solenoid is much larger than the field in an air-core solenoid carrying the same current. Reason (R): The ferromagnetic material has mu_r >> 1, so B = mu_r * mu0 * H is enormously amplified compared to B0 = mu0 * H for air.

Reasoning Options

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Chapter sections

Chapter 5: Magnetism and Matter | Assertion-Reason

Assertion (A): The net magnetic flux through any closed surface is always zero. Reason (R): Magnetic monopoles do not exist, so there are no sources or sinks of magnetic field B.

Assertion (A): A bar magnet placed in a uniform magnetic field experiences zero net force. Reason (R): In a uniform field, the forces on the north and south poles of the bar magnet are equal in magnitude and opposite in direction, cancelling each other.

Assertion (A): Magnetic field lines always form continuous closed loops. Reason (R): Magnetic field lines begin from the north pole and end at the south pole of a magnet.

Assertion (A): When a bar magnet is cut into two halves, we get two isolated magnetic poles — one north and one south. Reason (R): Magnetic monopoles do not exist in nature; isolated north or south poles cannot be created.

Assertion (A): A superconductor is a perfect diamagnet. Reason (R): For a superconductor, chi = -1 and mu_r = 0, so the external magnetic field is completely expelled from its interior.

Assertion (A): Two magnetic field lines can intersect each other at a point of strong magnetic field. Reason (R): At a point of intersection, the direction of the net magnetic field would be ambiguous.

Assertion (A): The magnetic potential energy of a dipole is minimum when the dipole moment is parallel to the external field. Reason (R): Potential energy U = -m.B = -mB cos(theta) is minimum when theta = 0 degrees, giving U = -mB.

Assertion (A): The magnetic field lines inside a toroid form complete closed loops entirely within the toroid. Reason (R): Each field line loop inside the toroid encloses a region through which a current is passing.

Assertion (A): A diamagnetic substance moves from the stronger to the weaker region of an external magnetic field. Reason (R): Diamagnetic substances have a small positive magnetic susceptibility.

Assertion (A): Magnetic susceptibility chi of a paramagnetic material depends on temperature. Reason (R): Both chi and mu_r of a paramagnetic material depend on the material and on the sample temperature; lowering temperature increases susceptibility.

Assertion (A): Diamagnetism is present in all substances. Reason (R): The mechanism of diamagnetism (Lenz's law effect on orbital electrons) operates in every atom that has orbiting electrons.

Assertion (A): A bar magnet and a current-carrying solenoid produce similar magnetic field patterns. Reason (R): The axial field of a finite solenoid at large distances has the same mathematical form as the axial field of a bar magnet.

Assertion (A): A magnetic needle placed in a uniform field experiences zero net force. Reason (R): Magnetic force on a moving charge is always perpendicular to the velocity, so no net translational force acts on the needle.

Assertion (A): When a ferromagnet is heated above its Curie temperature, it becomes paramagnetic. Reason (R): Above the Curie temperature, thermal energy destroys the cooperative domain alignment, and individual atomic dipoles become randomly oriented.

Assertion (A): The magnetic field lines do not represent lines of force on a moving charged particle. Reason (R): The magnetic force on a moving charge (F = qv x B) is always perpendicular to B, not along the field line.

Assertion (A): Alnico is used for making permanent magnets. Reason (R): Alnico is a soft ferromagnetic material whose magnetisation disappears on removal of the external field.

Assertion (A): A system can have a net magnetic moment even when its net electric charge is zero. Reason (R): Magnetic moments arise from circulating currents (moving charges), and the average of magnetic moments from various current loops may be non-zero even when net charge is zero.

Assertion (A): The equatorial field of a bar magnet at distance r is equal in magnitude to its axial field at the same distance. Reason (R): Both equatorial and axial fields of a short bar magnet are inversely proportional to r^3.

Assertion (A): For a paramagnetic material, both chi and mu_r are greater than 1. Reason (R): For paramagnetic materials, chi is small and positive (0 < chi < epsilon), so mu_r = 1 + chi is slightly greater than 1.

Assertion (A): The magnetic field inside a ferromagnetic core of a solenoid is much larger than the field in an air-core solenoid carrying the same current. Reason (R): The ferromagnetic material has mu_r >> 1, so B = mu_r * mu0 * H is enormously amplified compared to B0 = mu0 * H for air.

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