Chapter 2 — Electrostatic Potential and Capacitance

Chapter 2 of NCERT Class 12 Physics Part I covers electrostatic potential and capacitance, explaining how electric potential is the work done per unit positive charge in bringing it from infinity to a point, and how capacitors store energy using the relation C = Q/V.

This chapter introduces electrostatic potential as the work done per unit positive charge (without acceleration) brought from infinity to a given point in an electric field. It derives the potential due to a point charge V(r) = Q/(4πε₀r), a dipole, and a system of charges using the superposition principle. Equipotential surfaces are described as always perpendicular to the electric field. The chapter covers electrostatics of conductors, dielectric polarisation, and capacitors — including the parallel plate capacitor with capacitance C = ε₀A/d, combinations in series and parallel, the effect of dielectrics (C = KC₀), and energy stored in a capacitor U = (1/2)CV².

1. 01Electrostatic potential at a point equals the work done by an external force per unit positive charge in bringing it from infinity to that point, with potential at infinity taken as zero.
2. 02Potential due to a point charge Q at distance r is V = Q/(4πε₀r); for a dipole it falls off as 1/r² and depends on the angle with the dipole moment.
3. 03Equipotential surfaces are always perpendicular to the electric field; no work is done moving a charge along an equipotential surface.
4. 04Inside a conductor the electric field is zero, potential is constant throughout, and any excess charge resides only on the outer surface (electrostatic shielding applies to cavities).
5. 05Capacitance C = Q/V depends only on geometry; for a parallel plate capacitor C = ε₀A/d, and inserting a dielectric of constant K increases it to C = Kε₀A/d.
6. 06Energy stored in a capacitor is U = Q²/(2C) = (1/2)CV² = (1/2)QV, and the energy density of an electric field is u = (1/2)ε₀E².