JEE Main Physics Electrostatics 2027: Gauss's Law, Potential & Capacitors
Coulomb's law, dipoles, Gauss's law results, potential and capacitors with dielectrics, taught with worked examples and the battery-connected trap.
Edurack
September 28, 2026
Electrostatics is the doorway to all of electricity and magnetism, and one of the most reliable chapters in JEE Main Physics. It runs on a compact toolkit: Coulomb's law, Gauss's law, potential and capacitance. Learn the standard results and most questions become quick substitutions.
Symmetry is your shortcut: pick the right Gauss surface and the integral disappears.
Chapter at a Glance
| Snapshot | Detail |
|---|---|
| NTA unit | Unit 11 of 20 — Electrostatics |
| Priority (trend-based) | High |
| Typical question style | Formula-driven numericals on fields, potential and capacitor networks |
| Best first step | Learn the Gauss's law results table, then capacitor cases |
Priority reflects past-paper trends, not an official NTA weightage.
What the NTA Syllabus Covers
- Electric charges, conservation of charge, Coulomb's law, superposition and continuous charge distributions
- Electric field, field lines, dipole and its field, torque on a dipole
- Electric flux and Gauss's law: infinite wire, infinite sheet, thin spherical shell
- Electric potential, equipotential surfaces, potential energy of charges and dipoles
- Conductors, insulators, dielectrics, capacitors, combinations and stored energy
Master These Topics
1. Coulomb's Law and the Electric Field
The force between point charges is F = k q₁q₂ / r², with k = 9 × 10⁹ N·m²/C². Field of a point charge: E = kq / r².
Worked example: Two 1 μC charges 3 cm apart: F = 9 × 10⁹ × 10⁻¹² / (9 × 10⁻⁴) = 10 N.
An electric dipole (charges ±q, separation 2a, moment p = q × 2a) has axial field 2kp/r³ and equatorial field kp/r³ (far away). Torque in a uniform field is τ = pE sinθ, and potential energy is U = −pE cosθ.
2. Gauss's Law: The Standard Results
Φ = q_enclosed / ε₀. Memorise these:
| Source | Field |
|---|---|
| Infinite line charge (λ per length) | λ / (2πε₀r) |
| Infinite plane sheet (σ per area) | σ / 2ε₀ |
| Thin spherical shell, outside | kq / r² |
| Thin spherical shell, inside | 0 |
Worked example: A shell carries 10 nC with radius 10 cm. At 20 cm from the centre, E = 9 × 10⁹ × 10 × 10⁻⁹ / 0.04 = 2250 N/C. Inside the shell the field is zero.
Trap: Field inside a charged conducting shell is zero, but potential inside is constant and not zero.
3. Potential and Potential Energy
Potential of a point charge is V = kq / r, and it is a scalar, so add contributions algebraically. Potential energy of two charges is U = kq₁q₂ / r. Field is the negative gradient of potential, so it points from high to low potential and is perpendicular to equipotential surfaces.
4. Capacitors and Dielectrics
Parallel plate capacitor: C = ε₀A / d; with a dielectric of constant K, C = Kε₀A / d. Energy stored: U = ½CV² = Q²/2C.
- Series:
1/C = 1/C₁ + 1/C₂. Parallel:C = C₁ + C₂. - 6 μF and 3 μF in series give 2 μF. In parallel they give 9 μF.
Inserting a dielectric:
| Quantity | Battery connected (V fixed) | Battery removed (Q fixed) |
|---|---|---|
| C | × K | × K |
| Q | × K | unchanged |
| V | unchanged | ÷ K |
| U | × K | ÷ K |
Common Traps to Avoid
- Adding potentials as vectors. Potential is a scalar, field is a vector.
- Mixing up battery-connected and battery-disconnected cases for dielectrics.
- Assuming potential is zero wherever field is zero.
- Forgetting that series capacitors share charge and parallel capacitors share voltage.
60-Second Revision Sheet
F = kq₁q₂/r²,E = kq/r²,V = kq/r- Dipole: axial
2kp/r³, equatorialkp/r³,τ = pE sinθ - Wire
λ/2πε₀r; sheetσ/2ε₀; shell outkq/r², in 0 C = ε₀A/d,U = ½CV²; dielectric multiplies C by K
Your Study Plan
- Day 1: Coulomb's law with vector superposition.
- Day 2: Gauss's law applications and shell problems.
- Day 3: potential, energy and dipole problems.
- Day 4: capacitor networks and dielectric cases, timed set.
Practice Electrostatics Questions Free → (opens in a new tab)
Continue Your Physics Journey
- Previous chapter: Oscillations & Waves
- Next chapter: Current Electricity
- All 20 JEE Main Physics chapters
- Complete JEE Main Syllabus 2027 guide
Frequently Asked Questions
Is Electrostatics important for JEE Main?
Yes, it is one of the most consistent chapters, often giving numerical value questions on capacitors and field calculations.
What is the field inside a charged conducting shell?
Zero everywhere inside, while the potential there equals the constant value at the surface.