GEN-PHYSICS-LESSON-1-4

General Physics 2

Unit Topics

• Electricity and Magnetism: The Art of Conserving Electricity

  • Lesson 1: Electric Charge and Static Electricity

  • Lesson 2: Coulomb's Law

  • Lesson 3: Electric Field

  • Lesson 4: Electric Potential

Lesson 1: Electric Charge and Static Electricity

Atoms & Electricity

• All matter is composed of atoms containing electrons, protons, and neutrons.

• Neutral Objects: Contain equal numbers of electrons and protons.

• Charged Objects: Imbalance in the number of electrons and protons results in an electrical charge. Neutrons do not participate in electric interactions.

Electric Charge

• An object with more electrons than protons is negatively charged.

• An object with more protons than electrons is positively charged.

• The electric imbalance can be extremely small, e.g., 1 imbalance per 10 trillion particles.

Conservation of Electric Charge

• Electric charge is conserved: charge cannot be created or destroyed, only transferred.

• Charged objects exert electric forces on each other: Opposite charges attract, like charges repel.

Ways to Transfer Electric Charges

Charging by Friction

• Electrostatic Series: Rubbing materials together can result in charge transfer, determined by their position in the series.

• Example: Rubbing rubber with fur can produce a negative charge on rubber.

Charging by Conduction

• Occurs when a neutral object contacts a charged object.

• Excess electrons from the charged object may transfer to the neutral one (if negative).

• If both objects are conductive spheres, they will share equal charge after contact.

• Charge resides on the surface due to electron repulsion.

Charging by Induction

• A charged object is brought near (not touching) a neutral object, which is connected to a distant object (e.g., Earth).

• This produces a redistribution of charge, resulting in the neutral object acquiring an opposite charge.

Static Electricity

• Defined as an imbalance of electric charge within or on the surface of a material.

Lesson 2: Coulomb's Law

Coulomb's Law Summary

• Describes the force between two point charges (F):

  • Formula: F = k (q1 * q2) / r²

  • Where k is Coulomb's Constant (9.0 x 10⁹ Nm²/C²)

  • Charge relationships:

    • Force is stronger as distance decreases.

Example Calculation

• For two 3C charges, at a distance of 50 cm, the force can be calculated using the formula:

  • F = k (q1 * q2) / r², yielding F = 0.324 N.

Lesson 3: Electric Field

Electric Field Definition

• A physical field surrounding charged particles exerting forces on other charges.

• Visualized as lines indicating direction (attracting or repelling).

Electric Field Strength

• Defined as the force per charge experienced by a test charge.

• Units: Newtons per Coulomb (N/C).

Important Equations

• Electric Field Strength formula: E = F / q

• Coulomb’s Law: F = k (q1 * q2) / r²

Electric Field Lines

• Visual representation of electric fields, showing direction and strength.

• Lines do not cross; proximity of lines indicates strength.

• By convention, lines point away from positive charges and toward negative ones.

Lesson 4: Electric Potentials

Importance of Electric Potentials

• Electric potential energy is crucial for daily life, derived from energy produced in generating plants.

• Voltage: Measure of electric potential energy needed to move a charge against an electric field.

Electric Potential Energy

• Energy required to move a charge against an electric field varies with distance and field strength.

• Example: Energy differences illustrated with light bulbs and electrical devices in their inactive states.

Electric Potential Difference (Voltage)

• Defined as the difference in electric potential between two points in an electric field.

• Voltage influences how much work is done on a charge to alter its potential energy.

Key Definitions

• Electric Potential (V): The electric potential energy per unit charge.

• Formula: V = U / q, where U is electric potential energy and q is the charge.