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Foundations of Physics

Ampere

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 A
Electromagnetism & Electronics

Ampere's Circuital Law

Maxwell's fourth equation (in magnetostatics) relating the integrated magnetic field around a closed Amperian loop to net electric current…

∮ B · dl = μ₀ I_enclosed T·m (Tesla-meters)
Classical Mechanics

Amplitude

The maximum magnitude of displacement from the equilibrium position in an oscillating or wave system.

A = x_max m
Optics

Angle of Deviation

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 Degrees (°)
Classical Mechanics

Angular Acceleration

The rate of change of angular velocity with respect to time.

α = dω/dt = τ / I rad/s²
Classical Mechanics

Angular Displacement

The angle through which a point or line rotates about a specified axis in a specified direction.

θ = s / r rad (radians)
Waves, Oscillations & Acoustics

Angular Frequency

A scalar measure of rotation or oscillation rate expressed in radians per unit time.

ω = 2π f = 2π / T rad/s
Classical Mechanics

Angular Momentum

The rotational analog of linear momentum, defined as the product of moment of inertia and angular velocity.

L = I ω = r × p kg·m²/s (J·s)
Classical Mechanics

Angular Velocity

The vector rate of change of angular displacement with respect to time.

ω = dθ/dt rad/s
Condensed Matter & Materials Physics

Annealing

A heat treatment process where a metal or glass is heated above its recrystallization temperature, held, and cooled slowly to relieve…

Heat T > T_recrystallization, Slow Cool °C (Annealing Temperature)
Nuclear & Particle Physics

Antimatter

Subatomic material composed of antiparticles that share identical mass, spin, and lifetime as normal matter particles but possess opposite…

e⁺ + e⁻ → 2 γ (511 keV gamma photons) Energy (MeV / GeV)
Classical Mechanics

Apparent Weight

The effective weight of a body, equal to the normal contact force supporting it in an accelerating frame.

W_app = m (g + a) N
Classical Mechanics

Archimedes' Principle

The principle stating that any object fully or partially submerged in a fluid experiences an upward buoyant force equal to the weight of…

Fb = m_fluid g = ρ_fluid V_displaced g N
Geophysics & Environmental Physics

Asthenosphere

The ductile, mechanically weak, deformable upper mantle layer located directly beneath the rigid lithosphere.

Seismic Low-Velocity Zone (LVZ): Depth ~ 100–250 km Pa·s (Mantle Viscosity ~10¹⁹–10²¹ Pa·s)
Optics

Astigmatism

A visual defect caused by non-spherical, asymmetric curvature of the cornea or lens, preventing rays in different planes from focusing at a…

Power difference = P_vertical - P_horizontal Diopters (D)
Optics

Astronomical Telescope

A refracting optical instrument consisting of a long-focal-length objective lens and short-focal-length eyepiece used to observe distant…

M = -f_obj / f_eye, Tube Length L = f_obj + f_eye Dimensionless (×)
Astrophysics, Cosmology & Relativity

Astronomical Unit (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 Astronomical Units (AU)
Geophysics & Environmental Physics

Atmospheric Aerosols

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 μg/m³ (Concentration)
Nuclear & Particle Physics

Atomic Nucleus

The extremely dense, positively charged central core of an atom containing virtually all of its mass, composed of protons and neutrons…

R ≈ R₀ A^(1/3), R₀ ≈ 1.2 fm fm (Femtometers = 10⁻¹⁵ m)
Quantum & Atomic Physics

Atomic Orbital

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) Dimensionless Spatial Function
Optics

Attenuation

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) dB/km
Biophysics & Medical Physics

Audiometry

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) dB HL (Decibels Hearing Level) & Hz
Quantum & Atomic Physics

Aufbau Principle

A rule governing electron configuration stating that electrons fill atomic orbitals of lower energy levels before occupying higher energy…

Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s... Dimensionless Rule
Quantum & Atomic Physics

Auger Effect

A non-radiative atomic process in which the filling of an inner-shell electron vacancy causes the ejection of a second outer-shell (Auger)…

E_Auger = E_K - E_L1 - E_L2,3 eV (Electron-Volts)