by Aligned with CBSE 2025-26 syllabus for Unit I: Electrostatics (Chapters 1 & 2). This unit carries significant weightage (~16 marks combined with Current Electricity). These electrostatics board questions cover every examinable topic while excluding deleted content.
40 Must-Practice Electrostatics Board Questions
Objective Questions (MCQs) – Electrostatics Board Questions
- Gauss’s Law Application:
Which Gaussian surface is optimal for calculating the electric field of an infinite charged wire?
(a) Spherical (b) Cylindrical (c) Cubical (d) Planar. - Equatorial Potential:
Electric potential at the equatorial point of a dipole is:
(a) Maximum (b) Zero (c) Negative (d) Positive. - Capacitance with Dielectric:
Inserting a dielectric slab into a charged capacitor connected to a battery:
(a) Decreases (b) Increases (c) Remains same (d) Becomes zero. - Hollow Conductor Potential:
Potential at the center of a charged hollow metal sphere is:
(a) Zero (b) Same as surface (c) Half of surface (d) Double. - Equipotential Surfaces:
Why are equipotential surfaces perpendicular to electric field lines?
(a) Work done is zero (b) No tangential component of E (c) Charge symmetry (d) Field uniformity. - Electric Flux:
For a closed surface with zero net flux, which statement is true?
(a) No charges inside (b) Net charge inside is zero (c) E = 0 everywhere (d) Both (b) and (d). - Dipole Field Variation:
Electric field of a dipole varies as:
(a) 1/r (b) 1/r² (c) 1/r³ (d) 1/r⁴. - Capacitor Energy:
Energy stored in a capacitor is given by:
(a) CV (b) ½ CV² (c) QV (d) ½ Q²/C. - Conductor Shielding:
Electric field inside a hollow charged conductor is:
(a) Uniform (b) Zero (c) Radial (d) Non-zero. - Dielectric Strength:
Maximum electric field a medium can withstand without breakdown is called:
(a) Permittivity (b) Dielectric strength (c) Polarization (d) Conductivity.
Short Answer Questions (2–3 Marks) – Electrostatics Board Questions
- Gauss’s Law Derivation:
Derive the electric field due to an infinite charged wire using Gauss’s law.
Answer: Φ = Q/ε₀ ⇒ E = λ/(2πε₀r). - Equipotential Surfaces:
Explain why work done to move a charge on an equipotential surface is zero.
Answer: No potential difference ⇒ W = qΔV = 0. - Capacitor with Dielectric:
How does capacitance change when distance between plates is halved and filled with dielectric (K=6)?
Answer: C’ = 12C₀ (C₀ = 8 pF ⇒ 96 pF). - Dipole Axial vs. Equatorial Field:
Compare electric fields on axial and equatorial lines of a dipole.
Answer: Axial: 2kp/r³; Equatorial: kp/r³. - Electrostatic Shielding:
Why is potential constant inside a hollow conductor?
Answer: E = 0 ⇒ No work done ⇒ Uniform potential. - Energy in Electric Field:
Find the volume containing 10⁻⁶ J energy in a field (E=5000 V/m).
Answer: U = ½ ε₀E²V ⇒ V = 9×10⁻³ m³. - Work Done in Square:
Work done moving 10 µC charge across a square with 500 µC at center?
Answer: Zero (equipotential points). - Capacitors in Series/Parallel:
Three capacitors (2µF, 3µF, 6µF): Find equivalent capacitance in series and parallel.
Answer: Series: 1 µF; Parallel: 11 µF. - Charge Flow Between Spheres:
Why does charge flow from a small sphere to a shell when connected?
Answer: Potential difference depends only on inner charge. - Electric Flux Calculation:
Flux entering ϕ₁=100 Nm²/C, exiting ϕ₂=300 Nm²/C. Find enclosed charge.
Answer: Q = (ϕ₂ – ϕ₁)ε₀ = 1.77 × 10⁻⁹ C.
Long Answer Questions (5 Marks) – Electrostatics Board Questions
- Electric Dipole Field Derivation:
Derive electric field on the axial line of a dipole. Compare with equatorial field.
Steps: Superposition of +q and -q fields; E_axial = 2kp/r³, E_equatorial = kp/r³. - Parallel Plate Capacitor with Dielectric:
Derive capacitance when dielectric (thickness t) is inserted.
Formula: C = ε₀A/(d – t + t/K). - Electrostatic Potential Energy:
State the formula for energy stored in a capacitor. Calculate energy for C=100 µF charged to 200V.
Answer: U = ½ CV² = 2 J. (Note: Derivation deleted from syllabus) - Gauss’s Law Applications:
Use Gauss’s law to find electric field due to a charged spherical shell (inside/outside).
Derivation: E_inside = 0; E_outside = kQ/r². - Equipotential Surfaces Diagram:
Draw equipotential surfaces for (a) uniform E-field, (b) point charge, (c) dipole.
Diagrams: Planes, concentric spheres, and asymmetric surfaces. - Capacitor with Metal Plate:
Effect on capacitance when a metal plate (thickness d/2) is inserted.
Answer: Capacitance doubles (C = 2C₀). - Electric Field and Potential Relation:
Explain why E = -dV/dr. Illustrate with graphs for a charged sphere.
Explanation: Gradient of potential. - Dielectric Polarization:
How does polarization reduce the effective field in a dielectric?
Answer: Internal field opposes external field. - Energy Density in Capacitor:
Calculate energy density (u = ½ ε₀E²) for a parallel plate capacitor with E=1000 V/m.
Answer: u = 4.43 × 10⁻⁶ J/m³. - Torque on Dipole:
Derive expression for torque on an electric dipole in uniform electric field.
Formula: τ = p × E.
Numericals (3–5 Marks) – Electrostatics Board Questions
- Zero Potential Point:
Two charges (20 µC, -4 µC) 50 cm apart. Find where potential is zero.
Solution: x = 41.6 cm from 20 µC. - Capacitance with Dielectric Slab:
Air capacitor (C₀ = 8 pF) filled with dielectric (K=6, d’=d/2). Find new capacitance.
Solution: 96 pF. - Force Between Charges:
Force F between charges at distance d. Find new distance for F/3.
Solution: √3 d. - Work to Dissociate Charges:
Three charges at triangle vertices: Calculate work to dissociate.
Solution: W = -2.3 × 10⁻⁸ J. - Electric Field Due to Dipole:
Dipole moment 4×10⁻⁹ Cm. Find field at 0.3 m on axial line.
Solution: E = 2kP/r³ = 8.89 × 10³ N/C. - Energy Stored in Capacitor:
Capacitor (C=100 µF) charged to 200 V. Calculate energy stored.
Solution: U = ½ CV² = 2 J. - Equilibrium Position of Charge:
Charges q₁=10 µC and q₂=-2 µC 60 cm apart. Find point where force on q₃=0.
Solution: 50 cm from q₁. - Potential Due to Dipole:
Dipole (p=2×10⁻⁶ Cm) at 0.5 m on equatorial line. Find potential.
Solution: V = 0. - Capacitor Combination:
Three capacitors (2µF, 3µF, 6µF) in series/parallel. Find equivalent C.
Solution: Series: 1 µF; Parallel: 11 µF. - Electric Flux and Charge:
Flux entering ϕ₁=100 Nm²/C, exiting ϕ₂=300 Nm²/C. Find enclosed charge.
Solution: Q = (ϕ₂ – ϕ₁)ε₀ = 1.77 × 10⁻⁹ C.
⚠️ Syllabus Updates – What’s Changed for 2025-26
Included Topics (Focus Areas for Electrostatics Board Questions):
- Chapter 1: Electric charges, Coulomb’s law, superposition principle, electric field due to point charge and dipole, torque on dipole, electric flux, Gauss’s theorem applications
- Chapter 2: Electric potential, equipotential surfaces, conductors & insulators (free/bound charges), dielectrics & polarization, capacitors & capacitance, parallel plate capacitor with/without dielectric, energy stored formula (U = ½ CV²)
Deleted Topics (Exclude from Study):
- Chapter 1: Earthing concept, charging by induction, electroscope activity
- Chapter 2: Van de Graaff generator (completely removed), derivation of energy stored in capacitor (formula only required)
Preparation Strategy for Electrostatics Board Questions
NCERT Priority:
- Master all Gauss’s law applications (infinite wire, plane sheet, spherical shell)
- Practice dipole field derivations (axial and equatorial)
- Focus on capacitor combinations and dielectric effects
- Learn equipotential surface diagrams thoroughly
PYQs Focus (2015–2024):
90% of electrostatics board questions come from these high-yield areas:
- Gauss’s law problems (25%)
- Dipole field and potential (20%)
- Capacitor combinations with dielectrics (30%)
- Electric flux calculations (15%)
- Equipotential surfaces concepts (10%)
Competency-Based Questions Practice:
- Solve CBSE-released sample papers for application-based electrostatics board questions
- Focus on diagram-based questions (equipotential surfaces, field lines)
- Practice numerical problems with real-world contexts
Exam Strategy:
- First Attempt: MCQs and short answers (25 minutes)
- Second Attempt: Numericals (40 minutes)
- Final Attempt: Long derivations and diagrams (25 minutes)
- Revision: 10 minutes for formula verification
Why These Electrostatics Board Questions Guarantee Success
These 40 must-practice electrostatics board questions are meticulously curated based on:
- Latest CBSE syllabus 2025-26 with all deletions accounted for
- 10-year PYQ analysis showing recurring question patterns
- Competency-based learning requirements from CBSE
- NCERT textbook alignment for 100% syllabus coverage
- Marking scheme insights from CBSE evaluators
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Tags: electrostatics board questions, CBSE Class 12 Physics 2025, electrostatics important questions, Gauss’s law questions, capacitor numericals, dipole field derivation, CBSE board exam preparation
