Overview
This lecture begins the Class 12 Physics first chapter "Electric Charges and Field," explaining the basic concepts of charge, its properties, conservation, and quantization.
Introduction to Electrostatics
- Electrostatics is a branch of physics that studies charges at rest and the forces and fields associated with them.
- Class 12 electromagnetism includes both electrostatics (charges at rest) and electrodynamics (charges in motion).
Basic Facts About Charge
- Charge is an intrinsic property of matter, like mass.
- The symbol for charge is ‘q’ and the SI unit is ‘Coulomb’ (C).
- Charge is a scalar quantity; it has no direction.
- Charges are of two types: positive and negative.
- Like charges repel each other, unlike charges attract each other.
Difference Between Charge and Mass
- Charge can be positive or negative, mass is always positive.
- Mass can change with speed, charge is not affected by speed.
- Charge always accompanies mass, but not every mass necessarily has charge.
Conservation of Charge
- Charge can neither be created nor destroyed; it can only be transferred.
- The total charge in an isolated system always remains constant.
- Conservation of charge also applies in radioactive and nuclear equations.
Quantization of Charge
- Quantization means charge is always found in fixed amounts (e, 2e, 3e, ...) and not in fractional values.
- The smallest independent charge is found on the electron: -1.6 × 10⁻¹⁹ C.
- Formula: q = n × e, where n = integer value.
Methods of Charging
- Charging by Conduction: Transferring charge by bringing two conductors into contact.
- Charging by Induction: Polarization and charge transfer by bringing close without touching.
- Charging by Friction: Transferring electrons by rubbing two insulator bodies.
Key Terms & Definitions
- Electrostatics — Study of stationary (at rest) charges.
- Charge (q) — Fundamental property of matter, SI unit Coulomb (C).
- Conservation of Charge — Total charge in an isolated system always remains the same.
- Quantization of Charge — Charge is always found in multiples of e (electron charge).
- Conduction — Charge transfer by direct touch.
- Induction — Inducing charge without touch.
- Friction — Charge transfer by rubbing, especially in insulators.
Action Items / Next Steps
- Revise the notes on quantization and conservation of charge studied today.
- Read the related theory in NCERT.
- Next topic: Coulomb’s Law.
- Ask for the next chapter or doubts in the comments.