CBSE Class 12 Physics Moving Charges and Magnetism PYQs Analysis (2021-2025)

Based on detailed analysis of last 5 years' papers. Perfect for 2026 Boards prep!

Key Trends

Weightage Breakdown: 1-2 MCQs/assertion-reason (1 mark), 1-2 short answers (2 marks), 1-2 long answers/numericals on force/torque/cyclotron (4-6 marks).
Repeated Topics: Biot-Savart law applications, Ampere’s circuital law (solenoid, toroid, straight wire), force on moving charge/current in B-field, Lorentz force, helical path of charged particle, cyclotron (frequency, radius), torque on current loop in uniform B-field, moving coil galvanometer, magnetic moment & dipole, force between parallel currents.
Difficulty: Medium; numericals on cyclotron radius & torque on loop are most repeated & scoring.
Changes: More numericals on helical motion & galvanometer sensitivity in 2023–2025.

Most Important and Repeated Questions

Question Example	Type/Marks	Years Repeated	Notes
Derive expression for force on a current-carrying conductor in uniform magnetic field. Also find torque on rectangular current loop (magnetic moment).	Derivation (3-4 marks)	2021, 2022, 2023, 2024, 2025	Repeated 5x; F = I (l × B), τ = m × B = m B sinθ (m = I A).
A charged particle (charge q, mass m, velocity v) enters uniform magnetic field B perpendicularly. Find radius & time period of circular path (cyclotron motion).	Numerical/Derivation (3 marks)	2021 Term 2, 2022, 2023, 2024	Repeated 4x; r = mv / (qB), T = 2πm / (qB), cyclotron frequency f = qB/(2πm).
Using Ampere’s circuital law, derive magnetic field inside a long solenoid and toroid.	Derivation (3-4 marks)	2022, 2023, 2024, 2025	Repeated 4x; Solenoid: B = μ₀ n I; Toroid: B = μ₀ N I / (2πr).
Assertion: Magnetic field lines form closed loops. Reason: No magnetic monopoles exist (div B = 0).	Assertion-Reason (1 mark)	2023, 2024, 2025	Repeated 3x; Both true, reason explains.
Find force between two parallel current-carrying wires (infinite length) separated by d (attractive/repulsive).	Short Answer (2 marks)	2021 Term 1, 2022, 2023, 2025	Repeated 4x; F/l = (μ₀ I1 I2)/(2π d); attractive if same direction, repulsive if opposite.
A proton/electron enters magnetic field at angle θ to B. Find radius of helical path & pitch.	Numerical (3 marks)	2022, 2023, 2024	Repeated 3x; r = (mv sinθ)/(qB), pitch = v cosθ × T = (2π m v cosθ)/(qB).
MCQ: The SI unit of magnetic moment is: (a) A m² (b) J/T (c) both (d) Wb/m²	MCQ (1 mark)	2021 Term 1, 2023, 2024	Repeated 3x; Answer (c) both (A m² = J/T).
Explain principle & working of moving coil galvanometer. How to convert it into ammeter/voltmeter.	Short Answer (3 marks)	2023, 2025	Repeated 2x; Torque τ = N I A B sinθ = kθ; Shunt for ammeter, series resistance for voltmeter.
Case-based: Charged particle in crossed E & B fields (velocity selector) or cyclotron application.	Case-Based (4 marks)	2023, 2025	Repeated 2x; v = E/B for undeflected path; cyclotron frequency independent of v.
Find magnetic field at centre of current-carrying circular loop or arc.	Short Answer (2 marks)	2021 Term 2, 2024	Repeated 2x; B = (μ₀ I)/(2R) at centre; for arc B = (μ₀ I θ)/(4π R).

Best Format for Preparation and Answering

Study Format: Memorize Biot-Savart/Ampere’s law applications (loop, solenoid, toroid). Practice cyclotron & helical path numericals daily. Draw force diagrams (right-hand rules).
Answer Format: Derivations: Choose Amperian loop → apply Ampere’s law → solve for B. Numericals: Use vector form (F = q(v × B)) or magnitude + direction. Always box final answer with units.
Tips: Cyclotron frequency/radius & torque on loop are highest repeat & marks. Master right-hand rules for direction. Time: 10–12 mins for 4–6 mark questions. Very scoring if diagrams & directions are correct.

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