CBSE Class 12 Physics Electrostatic Potential and Capacitance 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 numericals/derivations on capacitance/energy (3-5 marks).
Repeated Topics: Electric potential due to point charge/dipole/system of charges, equipotential surfaces, potential energy of dipole/system, capacitance of parallel plate/spherical/cylindrical capacitor, combination of capacitors (series/parallel), energy stored in capacitor, effect of dielectric on capacitance & energy.
Difficulty: Medium; numericals on combination of capacitors & energy with dielectrics are most repeated & scoring.
Changes: More numericals on dielectrics (partially filled capacitors) and energy calculations in 2023–2025.

Most Important and Repeated Questions

Question Example	Type/Marks	Years Repeated	Notes
Derive expression for capacitance of parallel plate capacitor with and without dielectric slab. Also find energy stored in capacitor.	Derivation (3-4 marks)	2021, 2022, 2023, 2024, 2025	Repeated 5x; C = ε₀A/d → C' = Kε₀A/d; Energy U = (1/2)CV² = Q²/(2C).
Find equivalent capacitance of network (series + parallel combination, usually 3–5 capacitors with values like 2μF, 3μF, 6μF).	Numerical (3 marks)	2021 Term 2, 2022, 2023, 2024	Repeated 4x; Reduce step-by-step (series: 1/C = 1/C1 + 1/C2; parallel: C = C1 + C2).
A parallel plate capacitor is charged to potential V. Dielectric slab of K is inserted. Find new capacitance, potential, charge, energy.	Numerical (3 marks)	2022, 2023, 2024, 2025	Repeated 4x; Connected to battery: V same, C → KC, Q → KQ, U → KU; Isolated: Q same, V → V/K, C → KC, U → U/K.
Assertion: Equipotential surfaces are perpendicular to electric field lines. Reason: Electric field is normal to equipotential.	Assertion-Reason (1 mark)	2023, 2024, 2025	Repeated 3x; Both true, reason explains (no work along equipotential).
Find electric potential at point due to dipole or system of charges (e.g., at axial/equatorial point of dipole).	Short Answer (2-3 marks)	2021 Term 1, 2022, 2023, 2025	Repeated 4x; V_axial = p/(4πε₀r²), V_equatorial = 0.
Calculate energy stored when two capacitors are connected in series/parallel and charged to V.	Numerical (3 marks)	2022, 2024	Repeated 2x; Series: C_eq = C1C2/(C1+C2), U = (1/2)C_eq V²; Parallel: C_eq = C1+C2.
MCQ: When a dielectric is inserted between plates of charged isolated capacitor, energy: (a) increases (b) decreases (c) remains same	MCQ (1 mark)	2021 Term 1, 2023, 2024	Repeated 3x; Answer (b) decreases (U = Q²/2C → C increases).
Derive capacitance of spherical capacitor (concentric spheres) or cylindrical capacitor.	Derivation (3 marks)	2023, 2025	Repeated 2x; Use Gauss's law → V = Q/(4πε₀) (1/a - 1/b) → C = 4πε₀ ab/(b-a).
Case-based: Given capacitor network with dielectrics partially filled, find equivalent C or energy.	Case-Based (4 marks)	2023, 2025	Repeated 2x; Treat partially filled as two capacitors in series.
A charge Q is distributed over two concentric spherical shells. Find potential at different regions.	Short Answer (2-3 marks)	2021 Term 2, 2024	Repeated 2x; V inside inner = constant, between shells varies, outside = kQ_total/r.

Best Format for Preparation and Answering

Study Format: Memorize capacitance formulas (parallel plate, spherical, cylindrical) & energy relations. Practice combination of capacitors & dielectric effect numericals daily. Draw equipotential surfaces for point charge/dipole.
Answer Format: Derivations: Show step-by-step (E → V = -∫E dl → C = Q/V). Numericals: Write formula → substitute values → include units. For dielectrics: Specify connected/isolated case.
Tips: Dielectric effect (battery connected vs isolated) & capacitor combination are highest repeat & marks. Always check if battery is connected (V constant) or isolated (Q constant). Time: 8–10 mins for 3–5 mark questions. Very scoring chapter.

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