Section 1: Electric Charge

Electric charge is quantized (q = ne), conserved in isolated systems, and additive. The elementary charge e = $1.6 \times 10^{-19}$ C is the smallest possible charge unit. Both positive and negative charges exist; charge is measured in coulombs (C). Charging methods include friction, induction, and conduction.

Section 2: Coulomb's Law

F = kq_{1}q_{2}/$r^{2}$ with k = $9 \times 10^{9}$ N $m^{2}$ $C^{-2}$. Dimensional formula of force: [M$LT^{-2}$]. The force is along the line joining charges, attractive for unlike, repulsive for like. Superposition: net force on any charge equals the vector sum of all pairwise Coulomb forces. Key numerical skill: converting μC to C, cm to m before substituting.

Section 3: Electric Field

E = kQ/$r^{2}$ (point charge), E = F/q_{0} (definition). Field lines never cross, originate from +q, terminate on −q. Special cases: ring on axis (E = kQx/($R^{2}$+$x^{2}$)^(3/2), maximum at x = R/√2), conducting sphere (E = 0 inside, E = kQ/$r^{2}$ outside), insulating sphere (E = kQr/$R^{3}$ inside, linear). The comparison of these two sphere cases is a prime NEET trap question.

Section 4: Electric Dipole

p = q·2l (vector, from −q to +q). Torque in uniform field: τ = pE sinθ. Potential energy of dipole: U = −pE cosθ. Fields at large r: E_axial = 2kp/$r^{3}$, E_eq = kp/$r^{3}$. Potential: V_axial = kp cosθ/$r^{2}$, V_equatorial = 0. The factor of 2 between axial and equatorial fields is the single most tested dipole fact.

Section 5: Gauss's Law

Φ = q_enc/ε_{0}. Choosing Gaussian surface: spherical for point/sphere charges, cylindrical for wire/rod, pill-box for plane. Results: infinite wire E ∝ 1/r; infinite plane E = constant; sphere E ∝ 1/$r^{2}$ outside, 0 inside (conductor), linear inside (insulator). Gauss's law derivation questions (for wire, plane, sphere) appear as 4–5 mark problems in NEET paper analysis.

Section 6: Electric Potential and Potential Energy

V = kQ/r; E = −dV/dr (note the negative sign — field points from high to low potential). Equipotential surfaces: always perpendicular to field lines. Work done on equipotential: W = q$\Delta V$ = 0. Potential due to system of charges: algebraic (scalar) sum. Potential energy U = kq_{1}q_{2}/r — sign determines whether configuration is bound (U < 0) or unbound (U > 0).

Section 7: Capacitors

C = Q/V = ε_{0}A/d. Dielectric: C = Kε_{0}A/d. Series: same Q, voltages add, 1/C_eq formula. Parallel: same V, charges add, C_eq formula. Energy: U = ½$CV^{2}$ = $Q^{2}$/2C = ½QV. Dielectric scenarios: connected battery → V fixed (C↑K, Q↑K, U↑K); disconnected battery → Q fixed (C↑K, V↓K, U↓K). Energy change explanation: connected — battery pumps extra charge; disconnected — electrical energy does mechanical work polarizing dielectric.