Physics: Fundamentals, Core Principles, Branches, and Important Topics

The branch of science concerned with matter, energy, space, time, and fundamental interactions between matter and energy is known as Physics. The scope of physics covers an extensive area of study, including topics in both quantum mechanics, which deals with the microscopic world, and general relativity, which describes the macroscopic universe. There are always several laws, formulas, derivations, units, and universal constants underlying any topic in physics.

This site includes all branches of physics based on domains. Understand the laws governing each physics branch, its key formulas with derivations, physical quantities, their units, and universal constants.

Fundamental Physical Constants

Physical constants are not just numbers plucked out of thin air. They describe the nature of physical reality itself and dictate the levels at which certain physical phenomena play a role. Physical constants are quantities that have a defined value regardless of the location within the universe.

Different Branches of Physics

Physics is a single, cohesive field. In the realm of Newtonian mechanics, from the ordinary size range to the tiny particles studied by quantum mechanics and all the way out to the expanding universe studied by cosmologists, there exists a connection between each one because of their common language of laws, formulae, constants, and calculations.

Important Topics of Physics

Comprehensive List of Physics Laws

Newton’s second law, Maxwell’s equations, and Schrödinger’s equation are not simply laws; they are profound statements reflecting the underlying symmetries and structure of reality. These equations are just their mathematical descriptions, while derivations show how they are logically related to each other. All physical laws can be considered generalised statements that are the result of observations and experiments and are mathematically derived.

Conservation Laws:

• Conservation of Energy

• Conservation of Linear Momentum

• Conservation of Angular Momentum

• Conservation of Electric Charge

• Conservation of Baryon Number

• Conservation of Lepton Number

• Conservation of Mass-Energy

Mechanics Laws:

• Newton's First, Second, and Third Laws of Motion

• Newton's Law of Universal Gravitation

• Kepler's Three Laws of Planetary Motion

• Hooke's Law

• Archimedes' Principle

• Pascal's Law

• Bernoulli's Theorem

• Boyle's Law

• Charles's Law

• Gay-Lussac's Law

• Avogadro's Law

• Ideal Gas Law

Thermodynamics Laws:

• Zeroth Law of Thermodynamics

• First Law of Thermodynamics

• Second Law of Thermodynamics

• Third Law of Thermodynamics

• Fourier's Law of Heat Conduction

• Newton's Law of Cooling

• Stefan-Boltzmann Law

• Wien's Displacement Law

Electromagnetic Laws:

• Coulomb's Law

• Gauss's Law (for electricity and for magnetism)

• Ohm's Law (V = IR)

• Joule's Law (H = I²Rt)

• Kirchhoff's Current Law (KCL)

• Kirchhoff's Voltage Law (KVL)

• Biot-Savart Law

• Ampere's Circuital Law

• Faraday's Laws of Electromagnetic Induction (First and Second)

• Lenz's Law

• Snell's Law of Refraction

• Law of Reflection

• Malus's Law

• Brewster's Law

• Maxwell's Four Equations (complete unification of electricity and magnetism)

Quantum and Modern Physics Laws:

• Planck's Radiation Law (E = hν)

• Einstein's Photoelectric Equation (KE_max = hν − φ)

• De Broglie's Hypothesis (λ = h/p)

• Heisenberg's Uncertainty Principle (Δx·Δp ≥ ħ/2)

• Pauli Exclusion Principle

• Bohr's Postulates (for Hydrogen atom)

• Radioactive Decay Law (N = N₀ e^(−λt))

• Rydberg Formula (atomic spectra)

• Postulates of Special Relativity (Einstein)

• Huygens' Principle

• Doppler Effect

• Graham's Law of Diffusion (rate of diffusion ∝ 1/√M)

• Beer-Lambert Law (I = I₀ e^(−μx)) Absorption of Radiation

Key Derivations in Physics

Derivations are the mathematical means by which a law is derived from principles into predictions. Derivation is critical because one must be able to reconstruct any formula based on principles.

Mechanics:

• Equations of uniformly accelerated motion (from definitions of velocity and acceleration)

• Work-energy theorem (from Newton's second law and integration)

• Conservation of energy (from the conservative force concept)

• Orbital velocity and escape velocity (from Newton's law of gravitation and energy conservation)

• Kepler's Third Law from Newton's law of gravitation (for circular orbits)

• Moment of inertia of common shapes (from the definition I = ∫r² dm)

• Parallel axis theorem (from the definition of moment of inertia)

Thermodynamics:

• Ideal gas pressure from kinetic theory (statistical mechanics approach)

• Relationship between RMS Speed and Temperature

• Carnot Efficiency from Reversibility and the Second Law

• Adiabatic Process Equation PVᵞ = Constant

• Maxwell Speed Distribution

Electromagnetism:

• Coulomb's law from Gauss's law

• Electric Field of an Infinite Sheet from Gauss's Law

• Self-inductance of a Solenoid from Faraday's Law and Biot-Savart Law

• Speed of Light from Maxwell's Equations

• Transformer Equation from Faraday's Law

• Energy stored in the inductor from the work done in building up the current

Optics:

• Laws of reflection and refraction from Huygens' principle

• Mirror formula from the geometry of reflection

• Lens formula from refraction at two spherical surfaces (Cartesian sign convention)

• Lens maker's formula from the thin lens equation

• Fringe width formula in YDSE from the geometry of the path difference

Modern Physics:

• Bohr radius and energy levels from Bohr's postulates and classical mechanics

• de Broglie wavelength from energy-momentum relations

• Radioactive decay law from a probability model

• Time dilation and length contraction from the Lorentz transformation

• Mass-energy equivalence from relativistic dynamics

Knowledge of physics requires more than simply rote learning of equations; instead, knowledge is acquired by comprehending the sources of equations, their application, the assumptions associated with them, and their relationships to other concepts. By grasping these relationships, the reader is able to gain much more than the ability to work problems; they gain understanding of the universe itself.