Physics

Diamagnetism is a magnetic response that opposes an applied field, giving materials negative magnetic susceptibility and weak repulsion from stronger-field regions.

A dielectric is a material that responds to an electric field primarily through polarization rather than sustained electrical conduction.

Diffraction is the spreading and interference of waves caused by apertures, obstacles, or spatial structure, underlying optical resolution and many methods of structural analysis.

Diffusion is the spreading of particles through random motion, producing net transport down concentration gradients under ordinary conditions.

The Dirac equation is a relativistic equation for spin-½ particles that explains electron spin and provides the foundation for describing fermions and antiparticles in quantum field theory.

Direct current is electric current that flows in one direction, used in batteries, electronic equipment, power conversion, and high-voltage transmission.

Optical dispersion is the frequency dependence of light propagation, producing effects such as color separation, wavelength-dependent delay, and pulse distortion.

A field-theoretic framework that describes physics at a specified scale through a systematic expansion, encoding unresolved shorter-distance effects in interaction coefficients.

The Einstein field equations describe how spacetime geometry responds to matter and energy, forming the dynamical foundation of general relativity.

Electric charge is a conserved property of matter that determines its electromagnetic interactions and occurs in positive and negative forms.

Electric current is the rate of net electric charge flow through a surface, measured in amperes and carried by charged particles.

An electric dipole is a separation of positive and negative charge, characterized by a vector dipole moment that determines its field and interaction with external fields.

An electric field is a vector field that describes the electric force per unit charge at each point in space and time.

Electric potential is electric potential energy per unit charge, describing electrostatic fields through a scalar quantity whose differences determine energy changes.

An electrical conductor is a material containing mobile charge carriers that allow electric current to flow under an applied electric field.

Electrical impedance is the complex, generally frequency-dependent ratio of voltage to current, describing both opposition to current and the phase relationship between them.

Electrical resistance measures the opposition of a material, component, or circuit to electric current, expressed as the ratio of voltage to current.

Electricity is the set of physical effects caused by electric charge, and the energy carrier that powers modern society.

Electromagnetic induction is the production of an electromotive force through changing magnetic flux or the motion of a conductor in a magnetic field.

Electromagnetic radiation transports energy and momentum through space as electromagnetic waves, with quantum interactions described in terms of photons.

The electromagnetic spectrum encompasses all electromagnetic radiation, ordered by wavelength, frequency, or photon energy, from radio waves to gamma rays.

Electromagnetism studies electric and magnetic fields, their interactions with charged matter, and the radiation they produce.

The electron is a stable, negatively charged elementary particle that governs chemistry, electricity and much of modern technology.

An electron hole is an unoccupied electronic state that behaves as a positively charged quasiparticle, especially in semiconductor valence bands.

A particle–antiparticle reaction in which an electron and a positron are converted into photons or other particles, conserving total energy and momentum.

Electronic band structure describes the allowed energies of electrons in a crystalline solid as functions of crystal momentum, providing a basis for understanding electrical and optical properties.

The electronvolt is a unit of energy equal to exactly 1.602176634 × 10⁻¹⁹ joules, defined by the energy gained by an electron accelerated through one volt.

Electrostatics studies stationary electric charges, their fields and potentials, and their interactions with conducting and insulating materials.

The electroweak interaction unifies electromagnetic and weak processes through a gauge theory whose symmetry is broken by the Higgs field.

The elementary charge is the positive magnitude of an electron’s charge and an exact defining constant of the International System of Units.

Energy is the quantity transferred between systems and conserved in isolated ones. It underpins nearly all of physics and much of the natural sciences.

Energy density measures energy per unit volume, or, in some engineering contexts, per unit mass, and is used to describe fields, fuels, and storage systems.

Energy quantization is the restriction of a physical system’s measurable energies to discrete values, rather than an uninterrupted range.

Enrico Fermi was an Italian-American physicist who developed quantum statistics and beta-decay theory and led the first controlled, self-sustaining nuclear chain reaction.

Enthalpy is a thermodynamic state function combining internal energy with pressure–volume energy, used to describe heat transfer, reactions, and fluid flow.

Entropy is a thermodynamic state quantity and a related statistical measure of microscopic multiplicity or uncertainty.

An equation of state relates the macroscopic properties of matter, describing how pressure, temperature, density, and other state variables depend on one another.

A family of physical principles linking universal free fall to the local equivalence of gravitation and acceleration.

Ernest Rutherford was a New Zealand-born physicist who established the nuclear model of the atom and pioneered research on radioactive decay and nuclear transformations.

Austrian physicist who developed wave mechanics and explored the foundations of quantum theory, biological order, and the relationship between mind and matter.

Evaporation is the conversion of a liquid into vapor at its surface, governed by energy supply, molecular interactions, and vapor transport.

The Faraday constant is the electric charge per mole of elementary charges, linking electrical measurements with chemical amounts in electrochemistry.

Faraday’s law relates induced electromotive force to changing magnetic flux and describes how time-varying magnetic fields generate circulating electric fields.

Feedback is a process in which a system’s output or consequences return to influence its subsequent behavior, enabling regulation, amplification, adaptation, or instability.

Fermi energy is the zero-temperature occupation boundary of a fermion system, setting a characteristic scale for its quantum behavior.

A Fermi surface is the boundary in momentum space that organizes the low-energy electronic states of a metal or other fermionic system.

Fermi–Dirac statistics describes the occupation of quantum states by identical fermions, incorporating the restriction that no two may occupy the same single-particle state.

A fermion is a particle with half-integer spin whose exchange statistics enforce the Pauli exclusion principle.

Ferromagnetism is magnetic ordering in which interacting magnetic moments develop spontaneous parallel alignment below a characteristic temperature.

A Feynman diagram is a graph that encodes a mathematical contribution to a perturbative calculation in quantum field theory and related areas of physics.

The fine-structure constant is a dimensionless physical constant that characterizes the strength of electromagnetic interactions and governs important features of atomic spectra and quantum electrodynamics.

The first law of thermodynamics expresses energy conservation by relating changes in a system’s energy to heat, work, and energy carried by matter.

A vector quantity describing an interaction that can change a body's momentum, produce rotation, or deform matter.

The French Academy of Sciences is a learned society founded in 1666 that promotes scientific research, provides expert advice, and supports scientific education and international cooperation.

Friction is resistance to relative motion between contacting surfaces or within materials, arising from interactions and deformation.

Fugacity is a pressure-dimensioned thermodynamic quantity that expresses chemical potential and enables equilibrium calculations for nonideal substances.

Italian astronomer, physicist, and mathematician whose observations and studies of motion helped shape the Scientific Revolution.

A gamma ray is a high-energy photon produced by nuclear transitions, particle interactions, or energetic astrophysical processes.

The gas constant relates temperature to molar energy and appears in the ideal gas law and many thermodynamic and chemical equations.

A framework describing physical interactions through fields with local transformation freedoms that leave observable predictions unchanged.