Chapter 4: Moving Charges and Magnetism Assertion-Reason Questions | physics Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): A stationary charged particle does not experience any force in a magnetic field. Reason (R): The magnetic force on a charge is given by F = q(v × B), which is zero when v = 0.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): The magnetic force on a moving charge does not change the speed of the particle. Reason (R): The magnetic force is always perpendicular to the velocity of the particle and hence does no work on it.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): The cyclotron frequency of a charged particle in a magnetic field is independent of its kinetic energy. Reason (R): The radius of the circular orbit increases with speed, keeping the time period and frequency constant.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): Parallel currents attract each other. Reason (R): Like charges also attract each other in electrostatics.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): The magnetic field inside an ideal long solenoid is uniform. Reason (R): Each turn of the solenoid acts as a circular current loop, and the net field is the vector sum of fields from all turns, which adds uniformly along the axis.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Magnetic field lines always form closed loops. Reason (R): Magnetic monopoles do not exist; every magnet has both a north and a south pole.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): The net force on a current-carrying rectangular loop placed in a uniform magnetic field is zero. Reason (R): The torque on the loop in a uniform magnetic field is also zero.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 8

Logic Check

Assertion (A): Ampere's circuital law cannot be used to find the magnetic field at the centre of a circular current loop. Reason (R): There is no Amperian loop through the centre of a circular loop along which the magnetic field is tangential and constant in magnitude.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 9

Logic Check

Assertion (A): Increasing the number of turns N in a moving coil galvanometer doubles both its current sensitivity and voltage sensitivity. Reason (R): Current sensitivity = NAB/k and voltage sensitivity = NAB/(kR), and both increase when N is doubled.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): A proton and an alpha particle moving with the same speed in the same magnetic field trace circular paths of different radii. Reason (R): The radius of a circular path in a magnetic field is r = mv/(qB), which depends on both mass and charge of the particle.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 11

Logic Check

Assertion (A): The magnetic field outside an ideal long solenoid is zero. Reason (R): The current in neighbouring turns of the solenoid flows in opposite directions on the exterior, causing their fields to cancel exactly outside.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): A circular current loop behaves like a magnetic dipole at large distances. Reason (R): The magnetic field on the axis of a circular loop falls as 1/x³ for x >> R, identical to the axial field of an electric dipole.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 13

Logic Check

Assertion (A): When a galvanometer is converted into a voltmeter, a high resistance is connected in series with it. Reason (R): A high series resistance ensures the voltmeter draws negligible current from the circuit and does not disturb the voltage being measured.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): The magnetic field at the centre of a semicircular current arc is half that at the centre of a full circular loop of the same radius carrying the same current. Reason (R): The straight portions of the wire on either side of the semicircle also contribute to the field at the centre.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 15

Logic Check

Assertion (A): A charged particle moving along the direction of the magnetic field traces a straight line (not curved). Reason (R): When velocity is parallel to B, the cross product v × B = 0, so the magnetic force is zero and the particle continues in a straight line.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): The force per unit length between two parallel wires carrying currents of 1 A each, separated by 1 m in vacuum, is 2 × 10⁻⁷ N/m. Reason (R): This is the defining condition for the SI unit of current, the ampere, as adopted in 1946.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): A current loop placed in a uniform magnetic field with its magnetic moment parallel to the field is in stable equilibrium. Reason (R): In this orientation, any small displacement produces a restoring torque that brings the loop back to the original position.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): Inside a long straight wire of radius a carrying uniform current, the magnetic field at r = a/2 is half the maximum field. Reason (R): Inside the wire, B ∝ r, so at r = a/2, B = Bmax/2, where Bmax occurs at the surface r = a.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 19

Logic Check

Assertion (A): Oersted's experiment showed that electricity and magnetism are related. Reason (R): Oersted observed in 1820 that a current-carrying wire deflected a nearby compass needle, demonstrating that moving charges produce a magnetic field.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 20

Logic Check

Assertion (A): An electron moving vertically downward in a horizontal northward magnetic field is deflected toward the east. Reason (R): For an electron moving downward (–z) in a northward field (+y), v × B = –ẑ × ŷ = x̂, and since the electron has negative charge, the force is in the –x (west) direction.

Reasoning Options

ByteNotes

Chapter sections

Chapter 4: Moving Charges and Magnetism | Assertion-Reason

Assertion (A): A stationary charged particle does not experience any force in a magnetic field. Reason (R): The magnetic force on a charge is given by F = q(v × B), which is zero when v = 0.

Assertion (A): The magnetic force on a moving charge does not change the speed of the particle. Reason (R): The magnetic force is always perpendicular to the velocity of the particle and hence does no work on it.

Assertion (A): The cyclotron frequency of a charged particle in a magnetic field is independent of its kinetic energy. Reason (R): The radius of the circular orbit increases with speed, keeping the time period and frequency constant.

Assertion (A): Parallel currents attract each other. Reason (R): Like charges also attract each other in electrostatics.

Assertion (A): The magnetic field inside an ideal long solenoid is uniform. Reason (R): Each turn of the solenoid acts as a circular current loop, and the net field is the vector sum of fields from all turns, which adds uniformly along the axis.

Assertion (A): Magnetic field lines always form closed loops. Reason (R): Magnetic monopoles do not exist; every magnet has both a north and a south pole.

Assertion (A): The net force on a current-carrying rectangular loop placed in a uniform magnetic field is zero. Reason (R): The torque on the loop in a uniform magnetic field is also zero.

Assertion (A): Ampere's circuital law cannot be used to find the magnetic field at the centre of a circular current loop. Reason (R): There is no Amperian loop through the centre of a circular loop along which the magnetic field is tangential and constant in magnitude.

Assertion (A): Increasing the number of turns N in a moving coil galvanometer doubles both its current sensitivity and voltage sensitivity. Reason (R): Current sensitivity = NAB/k and voltage sensitivity = NAB/(kR), and both increase when N is doubled.

Assertion (A): A proton and an alpha particle moving with the same speed in the same magnetic field trace circular paths of different radii. Reason (R): The radius of a circular path in a magnetic field is r = mv/(qB), which depends on both mass and charge of the particle.

Assertion (A): The magnetic field outside an ideal long solenoid is zero. Reason (R): The current in neighbouring turns of the solenoid flows in opposite directions on the exterior, causing their fields to cancel exactly outside.

Assertion (A): A circular current loop behaves like a magnetic dipole at large distances. Reason (R): The magnetic field on the axis of a circular loop falls as 1/x³ for x >> R, identical to the axial field of an electric dipole.

Assertion (A): When a galvanometer is converted into a voltmeter, a high resistance is connected in series with it. Reason (R): A high series resistance ensures the voltmeter draws negligible current from the circuit and does not disturb the voltage being measured.

Assertion (A): The magnetic field at the centre of a semicircular current arc is half that at the centre of a full circular loop of the same radius carrying the same current. Reason (R): The straight portions of the wire on either side of the semicircle also contribute to the field at the centre.

Assertion (A): A charged particle moving along the direction of the magnetic field traces a straight line (not curved). Reason (R): When velocity is parallel to B, the cross product v × B = 0, so the magnetic force is zero and the particle continues in a straight line.

Assertion (A): The force per unit length between two parallel wires carrying currents of 1 A each, separated by 1 m in vacuum, is 2 × 10⁻⁷ N/m. Reason (R): This is the defining condition for the SI unit of current, the ampere, as adopted in 1946.

Assertion (A): A current loop placed in a uniform magnetic field with its magnetic moment parallel to the field is in stable equilibrium. Reason (R): In this orientation, any small displacement produces a restoring torque that brings the loop back to the original position.

Assertion (A): Inside a long straight wire of radius a carrying uniform current, the magnetic field at r = a/2 is half the maximum field. Reason (R): Inside the wire, B ∝ r, so at r = a/2, B = Bmax/2, where Bmax occurs at the surface r = a.

Assertion (A): Oersted's experiment showed that electricity and magnetism are related. Reason (R): Oersted observed in 1820 that a current-carrying wire deflected a nearby compass needle, demonstrating that moving charges produce a magnetic field.

Unlock all Assertion-Reason Questions

Practice in Quiz Mode