Physics terms starting with I

Ice Core Analysis Geophysics & Environmental Physics Parts per thousand (‰ δ¹⁸O) / ppm (CO₂) The retrieval and paleoclimatological analysis of cylindrical ice samples extracted from deep polar ice sheets and alpine glaciers. Paleotemperature Proxy δ¹⁸O = ((¹⁸O/¹⁶O)_sample / (¹⁸O/¹⁶O)_standard - 1) × 1000‰

Ideal Gas Law Thermodynamics & Statistical Physics Pa·m³ = J The equation of state relating pressure, volume, temperature, and quantity of an ideal gas composed of non-interacting point particles. P V = n R T = N kB T

Impulse Classical Mechanics N·s (or kg·m/s) The vector quantity defined as the integral of a force over the time interval during which it acts, equal to the net change in momentum. J = ∫ F dt = Δp = m vf - m vi

Inclined Plane Classical Mechanics Dimensionless A simple machine consisting of a flat supporting surface tilted at an angle to the horizontal. MA = L / h = 1 / sin θ

Independent Variable Foundations of Physics Various The experimental condition or factor intentionally manipulated by the researcher to observe its effect on an outcome.

Inductive Reactance Electromagnetism & Electronics Ω (Ohms) The opposition offered by an inductor to alternating current flow, directly proportional to AC frequency and inductance. X_L = 2π f L = ω L

Inelastic Collision Classical Mechanics kg·m/s, J A collision in which total linear momentum is conserved, but total kinetic energy is not conserved. ∑ p_i = ∑ p_f, KE_final < KE_initial

Inertia Classical Mechanics kg The natural resistance of any physical object to any change in its velocity or state of motion. Quantified by Mass (m)

Inertial Confinement Fusion Plasma Physics g/cm² (Areal Density) & Mbar (Implosion Pressure) A fusion energy approach that uses intense laser or ion beam pulses to rapidly compress and heat a millimeter-scale fuel capsule to fusion ignition conditions. ρ R ≥ 1 g/cm² (Compressed Areal Density)

Inertial Mass Foundations of Physics kg A measure of an object's intrinsic resistance to changes in its velocity when subjected to a net force. m = F / a

Insolation Geophysics & Environmental Physics W/m² or kWh/m²/day The solar electromagnetic radiation power reaching a specified surface area per unit time. S = S₀ (R₀ / R)² cos Z

Intensive vs Extensive Properties Thermodynamics & Statistical Physics Various Classification of thermodynamic properties based on whether they depend on system size or amount of matter. Extensive: U, V, S, m, H; Intensive: T, P, ρ, μ

Interchange & Flute Instabilities Plasma Physics MHD Flute Mode Instability A magnetohydrodynamic (MHD) instability where high-pressure plasma and low-density magnetic fields interchange spatial positions in regions of unfavorable magnetic curvature. Bad Curvature Condition: (∇P) · (∇B) > 0

Internal Energy Thermodynamics & Statistical Physics J The total microscopic energy contained within a thermodynamic system, comprising kinetic energies of particle translational/rotational/vibrational motion and potential energies of intermolecular forces. U = (f/2) n R T (for ideal gas)

Intrinsic Semiconductor Condensed Matter & Materials Physics cm⁻³ (Carrier Density) An ultra-pure semiconductor crystal containing no significant dopant impurity species, where carrier concentration is determined purely by thermal excitation across the band gap. n = p = n_i = √(N_c N_v) e^(-E_g / (2 k_B T))

Ion Channels Biophysics & Medical Physics pS (Picosiemens Conductance) & pA (Current) Pore-forming transmembrane proteins that allow selective passive passage of specific ions down their electrochemical gradient. I_channel = g_channel (V_m - E_ion)

Ionization Energy Plasma Physics eV (Electron-Volts) The minimum energy required to detach an electron from a neutral atom or ion, initiating gas-to-plasma phase transformation. E_ion = h ν - K_e (Saha Ionization Equation)

Ionosphere Geophysics & Environmental Physics Electrons/m³ (Electron Density n_e) An ionized layer of Earth's upper atmosphere (~60 km to 1,000 km) where extreme solar UV and X-ray radiation ionize atmospheric gas atoms into free electrons and ions. Plasma Frequency f_p = (1 / 2π) √(n_e e² / (ε₀ m_e))

Ionospheric Scintillation Geophysics & Environmental Physics Dimensionless S₄ Index Rapid fluctuations in amplitude and phase of satellite radio signals caused by small-scale electron density irregularities in the ionosphere. Scintillation Index S₄ = √(⟨I²⟩ - ⟨I⟩²) / ⟨I⟩

Isobaric Process Thermodynamics & Statistical Physics J A thermodynamic change in state occurring under constant pressure conditions. ΔP = 0, W = P ΔV, Q = ΔH = n Cp ΔT

Isobars Nuclear & Particle Physics Dimensionless Species Nuclides of different chemical elements that share the exact same mass number A (total number of nucleons) while having different atomic numbers Z. A = Z + N = Constant

Isochoric Process Thermodynamics & Statistical Physics J A thermodynamic process occurring at constant volume, during which no mechanical boundary work is performed. ΔV = 0 ⇒ W = 0, Q = ΔU = n Cv ΔT

Isostasy Geophysics & Environmental Physics Meters (Crustal Root Depth) The state of gravitational equilibrium between Earth's lithospheric crust blocks floating at depths determined by their thickness and density upon the denser mantle. Airy Model: h_root = h_mountain (ρ_crust / (ρ_mantle - ρ_crust))

Isothermal Process Thermodynamics & Statistical Physics J A thermodynamic change in state occurring at a constant temperature throughout the system. ΔT = 0 ⇒ ΔU = 0, Q = W = n R T ln(V2/V1)

Terms starting with I