Advanced Notes from Electrostatics to Coulomb's law

What is Electrostatics?

• Definition: Branch of physics studying interactions between stationary electric charges.

• Focus: Behavior of electric fields and potential without the influence of moving charges or currents.

Basics of Electric Charge

• Definition: Static electricity results from the build-up of electric charge on an object's surface.

• Electric charge: A crucial physical quantity explaining static electricity effects.

Types of Electric Charge

• Only two charge types exist:

  • Positive charge

  • Negative charge

• Fundamental principles:

  • Like charges repel each other.

  • Unlike charges attract.

  • Force between charges decreases with increasing distance.

Conductors vs. Insulators

Conductors

• Definition: Materials allowing easy movement of electric charges.

• Key detail: Free electrons in metals are not bound, enabling movement.

Insulators

• Definition: Materials that prevent charge movement, securing electrons within atomic orbits.

Conductors vs. Insulators

• Good conductors (metals: copper, aluminum, gold, silver) are also good heat conductors.

• Insulators (wood, plastic, rubber) are generally poor heat conductors.

Charging Methods

Charging by Conduction and Induction

• Charging by rubbing (triboelectric charging): Result of friction between two different materials transferring electrons.

• Charging by induction: A charged object causes temporary charge separation in a neutral object without contact.

Coulomb’s Law

• Definition: Mathematical formula calculating electrostatic force between two charged particles (Coulomb's law).

• Named after Charles Coulomb (1736-1806), who proposed the formula.

Coulomb’s Law Formula

• Formula: F = k * (q1 * q2) / r²

• Parameters:

  • F: Electrostatic force between point charges q1 and q2.

  • k: Constant (8.99 × 10⁹ Nm²/C²).

  • r: Distance separating the charges.

Understanding Electrostatic Force

• Electrostatic force (Coulomb force): Amount and direction of attraction or repulsion between charged bodies.

• Nature: Vector quantity measured in Newtons.

Coulomb's Law Visual Representation

• Visual representation of forces acting on two charges (F12, F21).

Sample Problem for Coulomb's Law

• Example: Calculate electrostatic force between charges:

  • Given: q1 = 2 μC, q2 = -3 μC, separated by r = 0.1 m.

The Electric Field

• Definition: A vector field depicting force on a charged particle in space.

• Relation: Defined as force per unit charge, measured in N/C.

Electric Field Formula

• Formula: E = F/q

• Where:

  • E: Electric field strength.

  • F: Electrostatic force.

  • q: Small test charge.

Electric Field from Point Charge

• Magnitude of electric field due to point charge Q formula:

  • E = k * |Q| / r²

Representing Charges in Electric Field Equations

• Clarification of symbols:

  • q: Represents a point charge at a specific location.

  • Q: Represents the total charge of an object or system of charges.E: Represents the electric field strength, defined as the force per unit charge experienced by a positive test charge placed in the field.