Chapter 1 — Electric Charges and Fields

NCERT Class 12 Physics Chapter 1 covers Electric Charges and Fields, explaining how electric charges arise, Coulomb's law for forces between point charges, the concept of electric field and field lines, electric flux, Gauss's law, and electric dipoles — forming the foundation of electrostatics.

Chapter 1 of NCERT Class 12 Physics Part I introduces electrostatics — the study of forces, fields, and potentials due to static charges. It explains that electric charge comes in two types (positive and negative), follows three fundamental properties: additivity, conservation, and quantisation (q = ne, where e = 1.602 × 10⁻¹⁹ C). Coulomb's law gives the force between two point charges as F = (1/4πε₀)(q₁q₂/r²). The chapter introduces the electric field E, field lines, electric flux, Gauss's law (total flux = q/ε₀), electric dipoles, and applications including field due to an infinite line charge, plane sheet, and spherical shell.

1. 01Electric charges are of two types — positive and negative; like charges repel and unlike charges attract each other.
2. 02Charge is conserved (cannot be created or destroyed), additive (charges sum algebraically), and quantised: q = ne where e = 1.602 × 10⁻¹⁹ C.
3. 03Coulomb's law: the electrostatic force between two point charges q₁ and q₂ separated by distance r in vacuum is F = (1/4πε₀)(q₁q₂/r²), where ε₀ = 8.854 × 10⁻¹² C² N⁻¹ m⁻².
4. 04The electric field E at a point is the force per unit positive test charge placed there; for a point charge Q, E = (1/4πε₀)(Q/r²). Field lines start on positive charges and end on negative charges and never cross.
5. 05Gauss's law states that the total electric flux through any closed surface equals q/ε₀, where q is the total charge enclosed — a powerful tool for symmetric charge distributions.
6. 06An electric dipole (charges +q and –q separated by distance 2a) has dipole moment p = q × 2a; its field falls off as 1/r³ at large distances, faster than a point charge.