Browse All 842 Physics Terms A–Z

Ampere Foundations of Physics A The SI base unit of electric current, defined by fixing the elementary charge to e = 1.602176634 × 10⁻¹⁹ C. 1 A = 1 C / s

Ampere's Circuital Law Electromagnetism & Electronics T·m (Tesla-meters) Maxwell's fourth equation (in magnetostatics) relating the integrated magnetic field around a closed Amperian loop to net electric current passing through the loop. ∮ B · dl = μ₀ I_enclosed

Amplitude Classical Mechanics m The maximum magnitude of displacement from the equilibrium position in an oscillating or wave system. A = x_max

Angle of Deviation Optics Degrees (°) The angle between the direction of an incident light ray entering an optical element (like a prism) and its emerging direction. δ = i1 + i2 - A

Angular Acceleration Classical Mechanics rad/s² The rate of change of angular velocity with respect to time. α = dω/dt = τ / I

Angular Displacement Classical Mechanics rad (radians) The angle through which a point or line rotates about a specified axis in a specified direction. θ = s / r

Angular Frequency Waves, Oscillations & Acoustics rad/s A scalar measure of rotation or oscillation rate expressed in radians per unit time. ω = 2π f = 2π / T

Angular Momentum Classical Mechanics kg·m²/s (J·s) The rotational analog of linear momentum, defined as the product of moment of inertia and angular velocity. L = I ω = r × p

Angular Velocity Classical Mechanics rad/s The vector rate of change of angular displacement with respect to time. ω = dθ/dt

Annealing Condensed Matter & Materials Physics °C (Annealing Temperature) A heat treatment process where a metal or glass is heated above its recrystallization temperature, held, and cooled slowly to relieve internal stresses and increase ductility. Heat T > T_recrystallization, Slow Cool

Antimatter Nuclear & Particle Physics Energy (MeV / GeV) Subatomic material composed of antiparticles that share identical mass, spin, and lifetime as normal matter particles but possess opposite electric and quantum charges. e⁺ + e⁻ → 2 γ (511 keV gamma photons)

Apparent Weight Classical Mechanics N The effective weight of a body, equal to the normal contact force supporting it in an accelerating frame. W_app = m (g + a)

Archimedes' Principle Classical Mechanics N The principle stating that any object fully or partially submerged in a fluid experiences an upward buoyant force equal to the weight of displaced fluid. Fb = m_fluid g = ρ_fluid V_displaced g

Asthenosphere Geophysics & Environmental Physics Pa·s (Mantle Viscosity ~10¹⁹–10²¹ Pa·s) The ductile, mechanically weak, deformable upper mantle layer located directly beneath the rigid lithosphere. Seismic Low-Velocity Zone (LVZ): Depth ~ 100–250 km

Astigmatism Optics Diopters (D) A visual defect caused by non-spherical, asymmetric curvature of the cornea or lens, preventing rays in different planes from focusing at a single point. Power difference = P_vertical - P_horizontal

Astronomical Telescope Optics Dimensionless (×) A refracting optical instrument consisting of a long-focal-length objective lens and short-focal-length eyepiece used to observe distant celestial bodies. M = -f_obj / f_eye, Tube Length L = f_obj + f_eye

Astronomical Unit (AU) Astrophysics, Cosmology & Relativity Astronomical Units (AU) An astronomical unit of length defined as exactly 149,597,870,700 meters, representing the mean distance from Earth to the Sun. 1 AU = 149,597,870,700 m ≈ 1.496 × 10¹¹ m

Atmospheric Aerosols Geophysics & Environmental Physics μg/m³ (Concentration) Microscopic solid particles or liquid droplets suspended in the atmosphere originating from natural or human sources. Aerosol Optical Depth (AOD) τ, Direct/Indirect Radiative Effect

Atomic Nucleus Nuclear & Particle Physics fm (Femtometers = 10⁻¹⁵ m) The extremely dense, positively charged central core of an atom containing virtually all of its mass, composed of protons and neutrons bound by the strong nuclear force. R ≈ R₀ A^(1/3), R₀ ≈ 1.2 fm

Atomic Orbital Quantum & Atomic Physics Dimensionless Spatial Function A mathematical function describing the three-dimensional spatial wave function and probability distribution of an electron in an atom. ψ_n,l,m_l(r, θ, φ) = R_n,l(r) Y_l,m_l(θ, φ)

Attenuation Optics dB/km The loss of optical power or signal strength as light propagates through a medium or optical fiber. α = (10 / L) log10(P_in / P_out)

Audiometry Biophysics & Medical Physics dB HL (Decibels Hearing Level) & Hz The clinical evaluation and quantitative measurement of human hearing sensitivity across pure tone sound frequencies. Hearing Level dB HL = 20 log₁₀(P_measured / P_reference)

Aufbau Principle Quantum & Atomic Physics Dimensionless Rule A rule governing electron configuration stating that electrons fill atomic orbitals of lower energy levels before occupying higher energy levels. Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s...

Auger Effect Quantum & Atomic Physics eV (Electron-Volts) A non-radiative atomic process in which the filling of an inner-shell electron vacancy causes the ejection of a second outer-shell (Auger) electron. E_Auger = E_K - E_L1 - E_L2,3

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