Electric charge static electricity

Electric Charge and Static Electricity

Electricity is an essential concept in physics, and at its heart lies the idea of electric charge. This fundamental property governs how particles interact through electric forces.

What is Electric Charge?

Electric charge is an essential property of matter that enables it to interact through electric forces when other charged objects are nearby. It is not something visible or tangible but is responsible for electromagnetic interaction, one of the four fundamental forces in nature.

Primary Associations of Charge:

• Mass: Electric charge is always associated with matter, which means every charged particle also has mass. For example, an electron has both charge and mass.
• Sign Convention: Electric charges can be classified as either positive or negative, based on the type of particle. By convention:
  • Protons carry a positive charge (+e)
  • Electrons carry a negative charge (−e)

Properties of Electric Charge

1. Quantization of Charge: Charge exists in discrete amounts. Each electric charge exists as a whole-number multiple of the elementary charge, where \(e=1.6×10^{−19}\) coulombs.
   q = ±ne, where n is an integer. This means charge is not continuous but comes in packets.
2. Additivity of Charge: Electric charge behaves as a scalar and combines according to simple algebraic rules.
   In a group of charges, the net charge Q is obtained by summing all individual charges: Q = q₁ + q₂ + q₃ + ... + qₙ
3. Invariance of Charge: Electric charge is invariant under relativistic motion. The value of charge does not change regardless of the frame of reference or the speed of the observer. A moving electron still carries the same charge as a stationary one.

What is Static Electricity?

Static electricity is the build-up of electric charge on an object’s surface, typically caused by friction between dissimilar materials. This build-up remains stationary (static) until discharged.

Common Charging Methods:

• Friction: Rubbing two objects (like a glass rod and silk) causes electrons to transfer, resulting in opposite charges.
• Conduction: When a charged body comes into direct contact with a neutral object, part of its charge is transferred.
• Induction: A nearby charged object causes a redistribution of charges in a conductor without direct contact.

Coulomb’s Law

This law defines the electrostatic force between two point charges:

F = k × |q₁q₂| / r²

Where:

• F is the magnitude of force
• q₁ and q₂ are the point charges
• r is the distance between them
• k ≈ 9 × 10⁹ Nm²/C² is Coulomb’s constant

This force is attractive for opposite charges and repulsive for like charges.

Applications of Static Electricity

• Employed in laser printers and photocopiers where static charges help transfer toner onto paper surfaces.
• Applied in electrostatic precipitators to remove pollutants from air.
• Employed in automobile painting for even coating using charged paint particles.