Browse All 842 Physics Terms A–Z

Seebeck Effect Condensed Matter & Materials Physics μV/K (Seebeck Coefficient S) The direct conversion of a temperature gradient into an electrical voltage across a conductor or semiconductor. V = S ΔT = S (T_hot - T_cold)

Seismic Waves (P & S Waves) Geophysics & Environmental Physics km/s (Seismic Wave Velocities) Elastic body waves that propagate through Earth's interior during an earthquake, classified as Primary (P) waves and Secondary (S) waves. v_P = √((K + ⁴/₃ μ) / ρ), v_S = √(μ / ρ)

Seismology Geophysics & Environmental Physics m/s (Wave Speeds) The scientific study of earthquakes and the propagation of mechanical elastic waves through the Earth's interior and surface layers. v_p = √((K + ⁴/₃ μ) / ρ), v_s = √(μ / ρ)

Selection Rules Quantum & Atomic Physics Dimensionless Quantum Rules A set of quantum mechanical rules constraining allowed radiative transitions between atomic energy states. Δl = ±1, Δm_l = 0, ±1

Self-Inductance Electromagnetism & Electronics H (Henries = V·s/A) The property of an electrical conductor or coil whereby a change in current induces an opposing electromotive force in the conductor itself. E = -L (dI/dt), L = N Φ_B / I

Semiconductor Condensed Matter & Materials Physics S/m (Electrical Conductivity) A class of crystalline solids possessing electrical conductivity between that of conductors and insulators, controllable by temperature, light, or doping. σ = e (n μ_e + p μ_h), n_i = √(N_c N_v) e^(-E_g / (2 k_B T))

Semiconductor Diode Electromagnetism & Electronics A (Current), V (Voltage) A two-terminal semiconductor device formed by a p-n junction that allows electric current to flow easily in one direction while blocking it in reverse. I = I_s [exp(e V / (k_B T)) - 1]

Series Circuit Electromagnetism & Electronics Ω (Ohms) An electrical circuit topology in which components are connected end-to-end sequentially along a single continuous current path. R_total = R₁ + R₂ + R₃, I_total = I₁ = I₂ = I₃

Shape Memory Alloys Condensed Matter & Materials Physics % (Recoverable Superelastic Strain) A class of smart metallic alloys that can be deformed when cold, but return to their original pre-deformed shape when heated above a transition temperature. Reversible Austenite (High T) ↔ Martensite (Low T) Phase Shift

Shock Wave Waves, Oscillations & Acoustics Pa A extremely thin propagating pressure disturbance characterized by a nearly instantaneous jump in pressure, temperature, and density. P2 / P1 = 1 + (2γ / (γ + 1)) (M1² - 1)

SI Units Foundations of Physics Dimensionless The International System of Units (SI), the modern metric system used globally as the standard language of science and measurement.

Significant Figures Foundations of Physics Dimensionless The digits in a measured or calculated quantity that carry meaningful contribution to its measurement precision.

Simple Harmonic Motion Classical Mechanics m, rad/s Repetitive periodic motion where restoring force is directly proportional to displacement and acts toward the equilibrium position. x(t) = A cos(ω t + φ), ω = √(k/m)

Simple Machine Classical Mechanics Dimensionless A basic mechanical device that changes the direction or magnitude of an applied force. MA = F_out / F_in

Simple Microscope Optics Dimensionless (×) An optical magnifying instrument consisting of a single converging biconvex lens used to produce an enlarged, upright, virtual image. M = 1 + (D / f) (Image at near point D)

Singularity Astrophysics, Cosmology & Relativity Infinite Curvature / Density A region in spacetime where gravitational curvature and density become infinite, causing classical general relativity equations to break down. Lim (r → 0): R_μνρσ R^μνρσ → ∞

Solar Wind Plasma Physics km/s (Velocity) & cm⁻³ (Density) A continuous supersonic stream of fully ionized magnetoplasma (protons, electrons, alpha particles) expanding outward from the Sun's corona into interstellar space. v_sw ≈ 300–800 km/s, n_e ≈ 5 cm⁻³ at 1 AU

Solar Wind Interaction Geophysics & Environmental Physics Plasma Density & Velocity The plasma physics interaction between the Sun's supersonic coronal plasma stream and Earth's geomagnetic field. Bow Shock Formation (Supersonic Magnetosheath Plasma Flow)

Solenoid Electromagnetism & Electronics T (Tesla) A long helical coil of insulated wire that produces a uniform interior magnetic field when an electric current flows through it. B = μ₀ n I (where n = N / L)

Sonar Waves, Oscillations & Acoustics m Sound Navigation and Ranging—a technique utilizing acoustic wave propagation underwater to navigate, communicate, or detect objects. d = v_water t / 2

Sonic Boom Waves, Oscillations & Acoustics dB / Pa An explosive impulsive acoustic thunderclap heard on the ground when an object travels faster than the speed of sound. sin α = 1 / M (Mach Cone Angle)

Sound Intensity Waves, Oscillations & Acoustics W/m² The time-averaged rate of sound energy flow per unit area perpendicular to the direction of propagation. I = P / A = p_rms² / (ρ v)

Spacetime Continuum Astrophysics, Cosmology & Relativity 4D Manifold (3 Space + 1 Time) A 4D mathematical continuum combining 3D space and 1D time into a unified pseudo-Riemannian manifold. ds² = g_μν dx^μ dx^ν (4D Pseudo-Riemannian Manifold)

Spark Chamber Nuclear & Particle Physics Visual Spark Tracks A historic particle detector consisting of parallel metal plates filled with noble gas where high-voltage electrical sparks form along ionized particle tracks. High Voltage Spark Discharge along Ionized Tracks

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