Electrostatics

Electrostatics is the study of stationary electric charges. It involves the behavior of charges at rest, the forces they exert on one another, and the fields they create.

1. Existence of Charges in Matter

Matter is made up of atoms, which consist of a central nucleus (protons and neutrons) and orbiting electrons. There are two types of charges: positive (protons) and negative (electrons). Like charges repel each other, while unlike charges attract.

2. Charging a Body

• Friction: Rubbing two different materials (like glass and silk) causes electrons to move from one to the other.
• Contact (Conduction): A charged object touches a neutral conductor, transferring part of its charge.
• Induction: Charging a conductor without touching it by bringing a charged object nearby and providing a path for electrons to flow to or from the ground (earthing).

3. The Gold-Leaf Electroscope

An electroscope is an instrument used to detect the presence and nature of electric charge. It consists of a metal rod with a gold leaf attached at the bottom. When charged, the leaf diverges due to repulsion.

• Uses: To test if a body is charged, to identify the type of charge, and to test for conductivity.

4. Coulomb's Inverse Square Law

The force F between two point charges q₁ and q₂ is directly proportional to the product of their charges and inversely proportional to the square of the distance r between them:
F = (k · q₁ · q₂) / r²
Where k ≈ 9 × 10⁹ Nm²C^-2.

5. Electric Field and Potential

Electric Field Intensity (E): The force per unit positive charge at a point in the field. E = F / q = kQ / r². The unit is N/C or V/m.

Electric Potential (V): The work done in bringing a unit positive charge from infinity to a point in the field. V = kQ / r. The unit is the Volt (V).

6. Electric Flux and Charge Distribution

Electric flux lines represent the direction and strength of the electric field. They originate from positive charges and terminate on negative charges. On a conductor, charges always reside on the outer surface. For irregularly shaped conductors, the charge density is highest at sharp points (Action of Points).

7. Lightning and Lightning Conductors

Lightning is a massive electrostatic discharge between clouds or between a cloud and the ground. A lightning conductor is a metal rod with sharp spikes placed on top of buildings. It provides a low-resistance path for the charge to reach the ground safely, preventing damage through the 'action of points'.