Browse the dictionary
842 terms · page 27 of 36
Quantum Hall Effect
Condensed Matter & Materials Physics
Ω (Von Klitzing Constant R_K ≈ 25812.807 Ω)
A quantum mechanical version of the Hall effect observed in 2D electron gases at low temperatures and intense magnetic fields, where Hall resistance is quantized in integer multiples of h/e².
R_H = h / (ν e²), ν = 1, 2, 3...
Quantum Harmonic Oscillator
Quantum & Atomic Physics
eV or Joules
The quantum mechanical analogue of a classical harmonic oscillator, describing a particle bound in a parabolic potential well V(x) = ½ m ω² x².
E_n = (n + ½) ℏ ω, n = 0, 1, 2, 3...
Quantum Operators
Quantum & Atomic Physics
Varies by Observable
Linear mathematical operators that act on a wave function to yield physical observables (such as position, momentum, or energy).
p̂ = -i ℏ ∇, x̂ = x, Ĥ = -(ℏ² / (2m)) ∇² + V(x)
Quantum Superposition
Quantum & Atomic Physics
Dimensionless State Vector
A core principle of quantum mechanics stating that a quantum system can exist in a linear combination of multiple distinct quantum states simultaneously until measured.
|Ψ⟩ = α |0⟩ + β |1⟩, |α|² + |β|² = 1
Quantum Tunneling
Quantum & Atomic Physics
Dimensionless (Transmission Probability)
A quantum phenomenon where a particle passes through a potential energy barrier higher than the particle's kinetic energy.
T ≈ exp(-2 k L), k = √(2 m (V₀ - E)) / ℏ
Quark Flavor
Nuclear & Particle Physics
Quantum Numbers (S, C, B, T)
The quantum property that distinguishes the six fundamental types of quarks in the Standard Model.
6 Flavors: u, d, c, s, t, b
Quark-Gluon Plasma (QGP)
Plasma Physics
MeV (Transition Temperature)
A extreme phase of quantum chromodynamic (QCD) matter where hadrons melt into a deconfined state of free quarks and gluons at extreme temperatures.
T_deconfinement ≈ 150–170 MeV (~2 × 10¹² K)
Quarks
Nuclear & Particle Physics
Fractional Elementary Charge e
Fundamental spin-1/2 elementary particles that experience all four fundamental interactions and combine via the strong force to form hadrons.
q = +⅔ e (u, c, t), q = -⅓ e (d, s, b)
Quasar
Astrophysics, Cosmology & Relativity
Luminosity / Redshift z
An extremely luminous Active Galactic Nucleus (AGN) powered by gas accreting onto a supermassive black hole at the center of a distant galaxy.
L_quasar ~ 10⁴⁰ W (100–1000 times Milky Way Luminosity)
Quasi-neutrality
Plasma Physics
Dimensionless Balance Condition
The property of a plasma where positive ion charge density and negative electron charge density are nearly equal across spatial scales larger than the Debye length.
n_e ≈ ∑ Z_i n_i (For scale lengths L ≫ λ_D)
Radiation Dosimetry
Biophysics & Medical Physics
Gy (Gray = J/kg)
The subfield of medical physics quantifying and measuring ionizing radiation energy deposited in human tissues or phantom materials.
D = dĒ / dm (Absorbed Energy per Unit Mass)
Radiative Forcing
Geophysics & Environmental Physics
W/m² (Watts per square meter)
The net change in Earth's energy balance per unit area at the tropopause due to an environmental driver of climate change.
ΔF = F_incoming - F_outgoing
Radioactive Decay
Nuclear & Particle Physics
Bq (Bequerels = decays/s) or Ci (Curies)
The spontaneous process by which an unstable atomic nucleus loses energy by emitting ionizing radiation (particles or electromagnetic rays).
N(t) = N₀ e^(-λ t), A(t) = λ N(t)
Radioactive Tracer
Nuclear & Particle Physics
MBq or mCi (Administered Activity)
A chemical compound containing a radioisotope used to trace chemical or biological pathways through living organisms or industrial systems.
A(t) = A₀ e^(-λ t) (Short half-life diagnostic radiopharmaceutical)
Radiobiology
Biophysics & Medical Physics
Gy (Dose Response Units)
The study of the biological mechanisms and health effects of ionizing radiation acting on living cells and biological tissues.
DNA Double-Strand Breaks (DSB) ~ 35–40 per Gy per Cell
Radiocarbon Dating
Nuclear & Particle Physics
Years Before Present (BP)
A radiometric dating method that measures the residual decay activity of Carbon-14 in organic materials to determine their age up to ~50,000 years.
t = -(t_½ / ln 2) ln(A(t) / A₀), t_½ = 5730 years
Radiofrequency Plasma Heating
Plasma Physics
MW (RF Power Input)
A method of heating fusion plasma by launching high-power electromagnetic waves tuned to particle cyclotron or hybrid resonance frequencies.
Resonance Matching: ω_wave = ω_ce (ECRH) or ω_wave = n ω_ci (ICRH)
Radiometric Dating in Geology
Geophysics & Environmental Physics
Ma or Ga (Millions / Billions of Years)
A geochronological technique used to determine the absolute age of rocks and minerals by measuring radioisotope parent-to-daughter ratios.
t = (1 / λ) ln(1 + D / P) (Parent P → Daughter D)
Radiopharmaceuticals
Biophysics & Medical Physics
MBq or mCi (Administered Activity)
Pharmaceutical compounds containing radioactive isotopes administered to patients for target-specific diagnostic imaging or therapy.
Targeted Radionuclide Compound: Radiotracer + Carrier Molecule
Radiotherapy
Biophysics & Medical Physics
Gy (Gray = J/kg) Total Prescribed Dose
The clinical treatment of malignant cancer tumors using precisely targeted ionizing radiation beams to induce double-strand DNA damage in cancer cells.
Linear-Quadratic Cell Survival: S = exp(-α D - β D²)
Radius of Gyration
Classical Mechanics
m
The radial distance from a rotation axis at which total mass could be concentrated without altering the moment of inertia.
k = √(I / m)
Radon Gas Migration
Geophysics & Environmental Physics
Bq/m³ or pCi/L (Activity Concentration)
The environmental migration of radioactive Radon-222 gas from decaying uranium in rocks and soil into indoor building spaces.
Decay Chain: ²³⁸U → ²²⁶Ra → ²²²Rn (Half-life = 3.82 days)
Rainbow Formation
Optics
Degrees (°)
An optical meteorological phenomenon caused by reflection, refraction, and chromatic dispersion of sunlight inside raindrops.
θ_primary ≈ 42° (Red outer, violet inner)
Random Error
Foundations of Physics
Various
Unpredictable, non-repeatable fluctuations in experimental measurements that occur with equal probability in either direction.
Standard Error = σ / √N