Foundations of Physics

Introduction

Physics is the study of the natural world, aiming to describe and predict phenomena through models and theories. Classical physics refers to the frameworks developed before 1900, which remain foundational for understanding many everyday phenomena.

• Physicists build models of varying complexity to explain observations.

• Classical physics is divided into three main areas: Classical Mechanics, Thermodynamics, and Electricity and Magnetism.

• While classical physics is incomplete, it is highly effective for most day-to-day applications.

Classical Mechanics and Thermodynamics

Key Topics in Classical Mechanics

Physics 1 introduces classical mechanics and thermodynamics, two pillars of classical physics. Important topics include:

1. Kinematics (Chs 2-3): Study of displacement, velocity, and acceleration. Equations:

2. Newton's Laws of Motion (Chs 4-5): Fundamental laws describing forces and motion. Equation:

3. Energy (Ch 6): Includes kinetic and potential energy. Equations:

4. Conservation Laws (Chs 6-7): Conservation of energy, momentum, and angular momentum. Equations:

5. Newtonian Gravity (Ch 5): Universal law of gravitation. Equation:

6. Mechanical Waves (Ch 11): Study of wave phenomena in mechanical systems.

Classical Electricity and Magnetism

Introduction to Electromagnetism

Physics 2 introduces classical electricity and magnetism, focusing on the interactions between electric charges.

• Electrically neutral objects are composed of electric charges and can become charged.

• Classical electricity and magnetism describe the forces and interactions between these charges.

Lodestones and Amber

Historical Foundations

• Lodestones are naturally occurring, magnetized pieces of magnetite (iron ore). Historical Note: As early as 900 BCE, lodestones were known to attract iron. The term "magnet" comes from Magnesia, Greece.

• Amber is dried tree resin. Historical Note: Around 600 BCE, amber rubbed with fur could pick up hay, demonstrating static electricity. The Greek name for amber is elektron.

From Gilbert to Maxwell

Development of Electrodynamics

• William Gilbert published De Magnete in 1600, pioneering the study of magnetism and electricity.

• Maxwell's A Treatise on Electricity and Magnetism (1873) formalized classical electrodynamics.

• Hertz (1889) demonstrated electromagnetic waves, integrating optics into electrodynamics.

Classical Electrodynamics

Maxwell's Theory

• Electric charges interact through electromagnetic fields.

• Electric charges produce electromagnetic fields and feel forces due to them.

• The electromagnetic field has two components: electric field and magnetic field.

• A stationary charge produces an electric field; a steady current produces a magnetic field.

• Time-varying fields produce each other: - A time-varying magnetic field produces an electric field. - A time-varying electric field produces a magnetic field.

• Accelerating charges produce electromagnetic waves.

Roadmap of Study

Topics to be Covered

• Electrostatics: Electric fields from stationary charges

• DC Circuits: Capacitance and resistance

• Magnetostatics: Magnetic fields from steady currents

• Induction: Electric fields from time-varying magnetic fields

• AC Circuits: Inductance

• Electromagnetic Waves

• Optics

Consequences and Applications

Atoms, Electricity, and Optics

• Atoms and Molecules: Atoms consist of negatively charged electrons and a positively charged nucleus, bound by the electromagnetic force. Intermolecular forces are electric in nature.

• Electricity: Enables creation, distribution, and storage of power; underpins electronic communication and biological processes.

• Optics: Light is an electromagnetic wave. Eyes and optical instruments manipulate light to form images.

Limitations of Classical Physics

Boundaries of Applicability

• Relative speeds must be much less than the speed of light. Otherwise, Special Relativity is required. Classical mechanics is the low-speed limit of relativity.

• Gravity must be weak. Otherwise, General Relativity is required. Newtonian gravity is the weak-gravity limit.

• Objects must be larger than atomic scale. Otherwise, Quantum Mechanics is required. There is correspondence between classical and quantum systems, but some quantum systems have no classical limit.

Modern Physics

Extension Beyond Classical Physics

• Modern physics covers phenomena at very high speeds and very small scales.

• Early quantum mechanics topics: - Thermal spectra - Line spectra - Photoelectric effect

• Modern atomic theory: - Atomic orbitals - Electron configuration - Periodic table

• Nuclear physics: - Radioactive decay