Physics

Electric arc A sustained electrical discharge through a gas that forms a hot, luminous plasma. Electric arcs power welding, cutting, lighting and furnaces and are distinct from sparks and glow…

Electric charge Electric charge is a fundamental property of matter carried by subatomic particles; it determines electromagnetic interactions, governs static electricity and electric currents, an…

Electric current Electric current is the directed movement of electric charge. This article explains its definition, units, types, measurement, common examples, and practical significance.

Electric field: concept, laws, history and practical applications Electric field An electric field describes how electric charges exert force in space. This article explains its definition, mathematical laws, historical development, key properties and common ap…

Electric Flux: Definition, Surface Integrals, Units, and Relation to Gauss's Law Electric flux Overview of electric flux: definition and computation via surface integrals and dot products, SI units and equivalents, and how flux through closed surfaces relates to enclosed cha…

Electric potential Electric potential is the electric potential energy per unit charge (measured in volts). It quantifies the work per charge required to move a test charge within an electric field a…

Electric power: definition, units, and applications Electric power Electric power is the rate at which electrical energy is transferred or converted. This article explains units, basic formulas, AC vs DC behavior, conversion to other forms, genera…

Electrical conductivity Measure of a material's ability to carry electric charge: units, symbols, microscopic causes, temperature and frequency effects, measurement methods, applications, and relation to…

Electrical conductor Material that permits the flow of electric charge; properties, common materials, uses, temperature effects, safety and distinctions from insulators, semiconductors and superconduct…

Electrical energy: definition, units, storage, and applications Electrical energy Overview of electrical energy: what it is, how it is measured, stored, transmitted, and distinguished from electrical power, with common units and practical considerations.

Electrical filament: function, materials, history, and uses Electrical filament A filament is a thin wire or element that emits light or electrons when heated or energized; used in incandescent lamps and vacuum tubes, commonly made of tungsten and shaped to ma…

Electrical impedance: definition, representations, frequency behaviour and applications Electrical impedance Comprehensive overview of electrical impedance: definition, complex and polar forms, component formulas, frequency dependence, energy behaviour, reflection and practical applicatio…

Electrical Resistance: Definition, Causes, Laws, and Practical Roles Electrical resistance Electrical resistance quantifies how strongly a material opposes electric current. Overview, Ohm’s law, resistivity, temperature effects, differences from conductance and impedance…

Electricity: Principles, Generation, Transmission, Uses, and Safety Electricity Comprehensive overview of electricity: what it is, how it behaves, methods of generation and transmission, practical uses, safety considerations, and historical highlights.

Electrocution: causes, effects, prevention, and history Electrocution Electrocution is injury or death caused by electric current passing through a living body. This article covers mechanisms, health effects, common sources, first aid, prevention and…

Electroluminescence: light emitted by electrical excitation Electroluminescence Electroluminescence is light produced when an electric current or strong electric field excites a material. It underpins LEDs, OLEDs and EL panels and depends on electronic transit…

Electromagnetic induction Electromagnetic induction is the generation of voltage or current in a conductor by a changing magnetic field; it underpins electric generators, transformers, induction heating, an…

Electromagnetic radiation: properties, spectrum, history and uses Electromagnetic radiation A concise encyclopedia overview of electromagnetic radiation: its nature, spectrum, history, practical uses and safety, with distinctions from mechanical waves.

Electromagnetic spectrum The electromagnetic spectrum is the complete range of electromagnetic radiation, from the longest radio waves to the shortest gamma rays, describing wavelengths, frequencies, inter…

Electromagnetism Electromagnetism studies electric and magnetic forces, fields, and their unification into electromagnetic theory; it explains light, electric currents, and many technologies from m…

Electron: properties, history, behavior and applications Electron A concise encyclopedia entry on the electron: its identity as an elementary charged particle, discovery, role in atoms and electricity, key properties and major uses in science and…

Electron cloud (atomic orbital model) Electron cloud A modern atomic model describing electrons as probability distributions (orbitals) around the nucleus; explains chemical behavior, spectroscopy, and periodic trends.

Electron hole (quasiparticle in solids) Electron hole An electron hole is the absence of an electron in a material's electronic structure. Treated as a positively charged quasiparticle, holes are central to conduction, doping, and rec…

Electronvolt: definition, uses, and common scales Electronvolt The electronvolt (eV) is a small unit of energy used in atomic, nuclear and particle physics. This article explains its definition, conversions, typical magnitudes, history, and re…

Electrostatics: principles, charging mechanisms, effects and applications Electrostatics Electrostatics studies electric charges at rest, the forces and fields they produce, how charges are created and neutralized, and practical consequences from dust adhesion to elect…

Elementary particle A concise, neutral overview of elementary (fundamental) particles: definitions, classification, key properties, historical development, examples and their roles in physics.

Ell (unit of length) Ell Traditional unit of length based on the forearm or elbow; varied regionally (English, Scottish, Flemish, Polish) and related to cubit, span and other anthropic measures.

Energy: concepts, forms, history, and uses Energy Energy is the capacity to produce change or do work. This article explains physical definitions, common forms, conservation laws, resources, conversion and storage, applications, a…

Energy level (electron orbitals and quantized states) Energy level Explanation of electronic energy levels: quantization, bound and continuum states, degeneracy, atomic and molecular examples, spectroscopy, and practical importance.

Energy transfer Movement of energy from one place, object, or system to another; includes conduction, convection, radiation and work; governed by conservation of energy and central to engineering…

Entanglement A concept describing linked states or involvements — most notably quantum entanglement, but also social, legal, or ecological forms where parts become correlated or entwined.

Entropy (thermodynamics, statistical mechanics, and information theory) Entropy Entropy quantifies unavailable energy and the number of microscopic configurations of a system. It appears in thermodynamics, statistical mechanics, chemistry, and information theo…

EPR paradox (Einstein–Podolsky–Rosen paradox) EPR paradox A 1935 thought experiment by Einstein, Podolsky and Rosen that challenged quantum mechanics' completeness, introduced entanglement, and motivated work on locality, hidden variables…

Equilibrium: balance of forces and states across science and systems Equilibrium Overview of equilibrium as a balanced, unchanging state in physics, chemistry, biology, economics and other fields; types, examples, history, and key distinctions.

Erg (unit of energy) Erg The erg is a small unit of energy from the centimetre–gram–second (CGS) system, equal to 10⁻⁷ joules; formerly common in physics and astronomy, now largely superseded by SI units.

Escape velocity Minimum speed needed for an object to break free from a celestial body's gravity without further propulsion, with context, formula, assumptions and practical implications.

Event horizon The event horizon is the boundary around a black hole beyond which nothing, not even light, can reach a distant observer; it is a central concept in general relativity and astrophy…

Exciton: the electron–hole quasiparticle in solids Exciton An exciton is a neutral quasiparticle formed when an electron binds to a positively charged hole. This entry explains types, properties, formation, detection, applications and rela…

Exotic atom — atoms with unusual constituent particles Exotic atom An exotic atom contains one or more ordinary constituents replaced by other particles (muons, pions, antiprotons, positrons). These short-lived systems probe nuclear structure, fun…

Explosion (rapid energy release) Explosion An explosion is a rapid release of energy that produces a sudden expansion, pressure or shock waves, heat and often gases. This article explains causes, types, history, uses and sa…

Fahrenheit (temperature scale) Fahrenheit A temperature scale and unit (°F) in which water freezes at 32° and boils at 212° (at sea level). Widely used in the United States and a few other countries; converts to Celsius by…

Fall (motion) A fall in motion is the downward movement of an object caused primarily by gravity, modified by air resistance and other forces; includes free fall, terminal velocity, and practica…

Farad (F): the SI unit of electrical capacitance Farad A farad is the SI unit of electrical capacitance, equal to one coulomb per volt. Used in electronics to quantify charge storage, from picofarads in circuits to farads in supercapac…

Faraday cage: principles, history, and practical uses Faraday cage A Faraday cage is a conductive enclosure that blocks external electric fields and electromagnetic interference. This article explains how it works, its history, typical uses, limit…

Faraday’s law of induction Faraday's law of induction A foundational law of electromagnetism describing how a changing magnetic environment produces an electromotive force; basis for generators, transformers, and many electrical devic…

Femtosecond: the 10⁻¹⁵ second and ultrafast phenomena Femtosecond A femtosecond equals 10⁻¹⁵ second. This article explains the timescale, comparisons with attoseconds, typical events measured in femtoseconds, generation and measurement methods, a…

Fermi-Dirac statistics Quantum statistical description of indistinguishable fermions obeying the Pauli exclusion principle; gives occupation probabilities of single-particle states and underlies electron…

Fermilab (Fermi National Accelerator Laboratory) Fermilab Fermilab is the U.S. Department of Energy's flagship particle physics laboratory near Chicago, known for the Tevatron collider, major neutrino programs, accelerator technology and…