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Moving Charges and Magnetism Class 12 Assertion Reason Questions 2026-27

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Moving Charges and Magnetism Class 12 Physics: Assertion–Reason Questions

CBSE 2026–27 · 30 original practice questions with answers and explanations

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Important: These are original practice questions prepared for Learn Revise Hub. They are not copied from CBSE board papers and should not be treated as predictions of examination questions. Always use the latest official CBSE curriculum and sample-paper material as the authority.

How to Answer Assertion–Reason Questions

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

Exam method: First test Assertion and Reason independently. Only after that decide whether the Reason actually explains the Assertion. Do not select A merely because both statements are true.

CBSE 2026–27 Scope Check

Moving Charges and Magnetism is Chapter 4 under Unit III, Magnetic Effects of Current and Magnetism. Unit III carries 17 marks collectively for Chapters 4 and 5; CBSE does not assign a separate fixed chapter-only weightage here.

This practice set focuses on magnetic force, motion of charged particles, crossed fields, Biot–Savart law for circular loops, Ampere's law for an infinitely long straight conductor, qualitative understanding of a long solenoid, force between parallel currents, torque and magnetic dipole, and moving-coil galvanometer applications.

30 Assertion–Reason Practice Questions

Q1. A charged particle enters a uniform magnetic field with its velocity perpendicular to the field.
Assertion (A): The magnetic force on the particle does no work.
Reason (R): The magnetic force is perpendicular to the instantaneous velocity of the particle.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q2. A charged particle moves in a uniform magnetic field with velocity perpendicular to the field.
Assertion (A): Its kinetic energy remains constant.
Reason (R): The magnetic force changes the direction of velocity but not its magnitude.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q3. A charged particle moves perpendicular to a uniform magnetic field.
Assertion (A): The radius of its circular path is directly proportional to its speed.
Reason (R): For perpendicular motion, r = mv/(|q|B).
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q4. A charged particle enters a uniform magnetic field with its velocity perpendicular to the field.
Assertion (A): The particle moves in a circular path if the magnetic field is uniform.
Reason (R): The magnetic force is perpendicular to the velocity and can provide the required centripetal force.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q5. A positive charge enters a magnetic field with velocity perpendicular to the field.
Assertion (A): Reversing the sign of the charge reverses the direction of magnetic force for the same velocity and magnetic field.
Reason (R): The magnetic force is q(v × B).
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q6. A charged particle moves parallel to a uniform magnetic field.
Assertion (A): The magnetic force on the particle is zero.
Reason (R): The angle between velocity and magnetic field is 0°.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q7. A charged particle enters crossed electric and magnetic fields with its velocity perpendicular to both fields.
Assertion (A): The particle can pass undeflected when qE = qvB in magnitude.
Reason (R): In the undeflected condition, electric and magnetic forces are equal in magnitude and opposite in direction.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q8. A long straight current-carrying conductor produces a magnetic field around it.
Assertion (A): At a fixed distance from a long straight conductor, increasing the current increases the magnetic field.
Reason (R): B = μ₀I/(2πr) for a long straight conductor.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q9. Consider two points at different distances from a long straight current-carrying wire.
Assertion (A): The magnetic field due to the wire decreases as distance from the wire increases.
Reason (R): For a long straight wire, B is proportional to r.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: C
A is true, but R is false; B is proportional to 1/r.
Q10. For a small current element, the Biot–Savart law gives the magnetic field contribution.
Assertion (A): The magnetic field contribution due to a current element is perpendicular to both the current-element direction and the line joining the element to the observation point.
Reason (R): The Biot–Savart expression contains the vector product dℓ × r̂.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q11. Consider the magnetic field at the centre of a circular current loop.
Assertion (A): Reversing the direction of current reverses the direction of the magnetic field at the centre.
Reason (R): The field direction follows the right-hand rule for the current direction.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q12. A circular current loop is placed in a uniform magnetic field.
Assertion (A): The torque on the loop is maximum when its magnetic moment is perpendicular to the magnetic field.
Reason (R): τ = mB sinθ, where θ is the angle between magnetic moment and magnetic field.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q13. A current loop is placed in a uniform magnetic field.
Assertion (A): The torque on the loop is zero when its magnetic moment is parallel to the magnetic field.
Reason (R): sin 0° = 0.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q14. Consider a current-carrying conductor in a magnetic field.
Assertion (A): The magnetic force on the conductor is zero when the conductor is parallel to the magnetic field.
Reason (R): F = BIL sinθ and sin 0° = 0.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q15. Two long parallel conductors carry currents in the same direction.
Assertion (A): The conductors attract each other.
Reason (R): Each conductor experiences a magnetic force due to the magnetic field produced by the other conductor.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q16. Two long parallel conductors carry currents in opposite directions.
Assertion (A): The conductors repel each other.
Reason (R): Reversing the current in one conductor reverses the direction of the magnetic force on that conductor.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q17. A long ideal solenoid carries steady current.
Assertion (A): The magnetic field inside an ideal long solenoid is approximately uniform away from its ends.
Reason (R): In the current CBSE syllabus, the straight-solenoid treatment is qualitative, emphasizing its approximately uniform interior field away from the ends.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q18. Ampere's circuital law is applied to a highly symmetric current distribution.
Assertion (A): Ampere's law is especially convenient when symmetry allows the magnetic field to be treated as constant along the chosen Amperian path.
Reason (R): The line integral of magnetic field around a closed path is related to the enclosed current.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: B
Both statements are true, but R does not by itself explain why the law is especially convenient for symmetric cases.
Q19. A moving-coil galvanometer is used to measure current.
Assertion (A): A galvanometer can be converted into an ammeter by connecting a suitable low resistance shunt in parallel with it.
Reason (R): The shunt provides an alternative path for most of the current while only a small current passes through the galvanometer coil.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q20. A galvanometer is converted into a voltmeter.
Assertion (A): A high resistance is connected in series with the galvanometer.
Reason (R): A high series resistance limits the current through the galvanometer when it is connected across a potential difference.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q21. The current sensitivity of a moving-coil galvanometer is increased.
Assertion (A): Increasing the number of turns of the coil can increase current sensitivity, if other relevant parameters remain unchanged.
Reason (R): Current sensitivity is proportional to the number of turns for a given magnetic field and torsional constant.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q22. A charged particle enters a uniform magnetic field with a velocity having both parallel and perpendicular components.
Assertion (A): The particle can follow a helical path.
Reason (R): The parallel velocity component remains unchanged while the perpendicular component produces circular motion.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q23. A charged particle moves in a uniform magnetic field with velocity having a component parallel to the field.
Assertion (A): The magnetic force changes the parallel component of velocity.
Reason (R): Magnetic force is perpendicular to the magnetic field.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: D
A is false, but R is true; the magnetic force does not change the velocity component parallel to B.
Q24. A charged particle completes circular motion in a uniform magnetic field.
Assertion (A): Increasing the magnetic field strength decreases the radius of the path for fixed momentum and charge magnitude.
Reason (R): r = p/(|q|B).
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q25. A proton and an electron enter the same uniform magnetic field with equal speeds, both perpendicular to the field.
Assertion (A): Their radii of circular paths are equal.
Reason (R): The magnitude of charge of a proton equals the magnitude of charge of an electron, but their masses are different.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: D
A is false, but R is true; r = mv/(|q|B), so the different masses give different radii.
Q26. A charged particle moves in a uniform magnetic field.
Assertion (A): Its momentum magnitude remains constant when the magnetic force is the only force acting.
Reason (R): A magnetic force is perpendicular to the particle's instantaneous velocity.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q27. A current-carrying circular coil has magnetic dipole moment m = NIA.
Assertion (A): For fixed N, I and A, increasing the number of turns increases the magnetic dipole moment.
Reason (R): The magnetic dipole moment of the coil is proportional to N.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q28. A charged particle is at rest in a region containing only a magnetic field.
Assertion (A): The magnetic field exerts no magnetic force on the particle.
Reason (R): The magnetic force is proportional to the particle's velocity.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q29. A moving-coil galvanometer is designed to be more sensitive to small currents.
Assertion (A): Increasing the number of turns of the coil can increase current sensitivity, if the other relevant parameters remain unchanged.
Reason (R): Current sensitivity is proportional to the number of turns for fixed magnetic field, coil area and torsional constant.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
Q30. A current-carrying conductor is placed in a uniform magnetic field.
Assertion (A): The direction of force on the conductor depends on the direction of current and magnetic field.
Reason (R): The force is given by F⃗ = I(L⃗ × B⃗).
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.
Answer: A
Both statements are true, and R correctly explains A.
High-value traps to revise: magnetic force does no work; speed can remain constant while velocity direction changes; r = mv/(|q|B); crossed-field undeflected motion; B ∝ I/r for a long straight wire; τ = mB sinθ; same-direction parallel currents attract; a galvanometer-to-ammeter conversion uses a parallel shunt; a galvanometer-to-voltmeter conversion uses high series resistance.

Quick Revision Formula Map

ConceptKey relation
Magnetic force on chargeF = |q|vB sinθ
Lorentz forceF⃗ = q(E⃗ + v⃗ × B⃗)
Circular radiusr = mv/(|q|B) = p/(|q|B)
Long straight wireB = μ₀I/(2πr)
Current-carrying conductorF⃗ = I(L⃗ × B⃗)
Current loop torqueτ = mB sinθ
Magnetic dipole momentm = NIA
Long solenoidQualitative treatment in the current CBSE 2026–27 syllabus

Continue the Chapter 4 Study Path

Chapter 4 Hub Notes Important Questions MCQs Case-Based Questions Chapter 3 — Current Electricity Chapter 2 — Electrostatic Potential and Capacitance Chapter 1 — Electric Charges and Fields

Source note: The chapter scope and unit-level assessment structure were checked against the official CBSE Class XII 2026–27 Physics curriculum. CBSE's official 2026–27 Class XII SQP/MS portal was also checked. The question design is original practice, informed by the assertion–reason format used in CBSE competency-focused Physics material.

For official updates, students should always verify the latest CBSE Academic curriculum, sample question paper and marking scheme.

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