Physics terms starting with E

Electrical Resistivity Electromagnetism & Electronics Ω·m (Ohm-meters) An intrinsic material property quantifying how strongly a material opposes the flow of electric current. ρ = R A / L = 1 / σ

Electro-osmosis Biophysics & Medical Physics m/s (Electro-osmotic Velocity) The motion of a liquid containing mobile ions through a porous biological membrane or microchannel driven by an applied electric field. v_eo = (ε_r ε₀ ζ / η) E (Smoluchowski Equation)

Electrocardiography (ECG) Biophysics & Medical Physics mV (Amplitude ~1 mV) & bpm (Heart Rate) A non-invasive diagnostic technique recording the spatial bioelectric potential changes produced by heart muscle depolarization and repolarization. Cardiac Dipole Vector P(t), Einthoven's Triangle Lead Vectors

Electroencephalography (EEG) Biophysics & Medical Physics μV (Microvolts ~10–100 μV) & Hz A non-invasive neurophysiological technique measuring electrical brain activity using surface scalp electrodes. Frequency Bands: Delta (1–4Hz), Theta (4–8Hz), Alpha (8–12Hz), Beta (12–30Hz)

Electromagnetic Spectrum Electromagnetism & Electronics Hz (Frequency), m (Wavelength) The continuous range of all frequencies and wavelengths of electromagnetic radiation, ordered from low-frequency radio waves to high-frequency gamma rays. c = f λ, E = h f

Electromagnetic Waves Electromagnetism & Electronics m/s (Velocity) Transverse self-propagating oscillations of coupled electric and magnetic fields traveling through space at the speed of light. c = 1 / √(μ₀ ε₀) ≈ 3 × 10⁸ m/s, E = c B

Electron Spin Quantum & Atomic Physics J·s (Spin Angular Momentum) An intrinsic form of angular momentum carried by elementary particles, independent of orbital spatial motion. S = √(s (s + 1)) ℏ, s = ½, S_z = ± ½ ℏ

Electroporation Biophysics & Medical Physics kV/cm (Electric Field Strength) A biophysical technique applying short, high-voltage electric field pulses to cells to temporarily increase cell membrane permeability by creating nanoscale aqueous pores. Critical Transmembrane Breakdown Voltage V_c ≈ 0.5–1.0 V

Elementary Charge Foundations of Physics C The fundamental electric charge carried by a single proton, or the absolute value of charge carried by a single electron. e = 1.602176634 × 10⁻¹⁹ C

Emissivity Thermodynamics & Statistical Physics Dimensionless The dimensionless ratio of thermal energy radiated by a surface to that radiated by an ideal blackbody at the exact same temperature. ε = E_surface / E_blackbody (0 ≤ ε ≤ 1)

End Correction Waves, Oscillations & Acoustics m An acoustic correction applied to resonance pipe lengths to account for displacement antinodes forming slightly outside the open pipe ends. e ≈ 0.6 r, L_effective = L + 0.6 r (One Open End)

Energy Foundations of Physics J The quantitative property that must be transferred to a physical system to perform work on it, or to heat it. E = mc²

Enriched Uranium Nuclear & Particle Physics Weight Percent (% ²³⁵U) Uranium in which the relative concentration of the fissile isotope Uranium-235 has been increased above its natural abundance (~0.72%). % U-235 Concentration (Low Enriched: 3–5%, High Enriched: >20%)

Enthalpy Thermodynamics & Statistical Physics J A thermodynamic potential defined as internal energy plus the product of pressure and volume, representing total heat content under constant pressure conditions. H = U + P V, ΔH = Q_p

Entropy Thermodynamics & Statistical Physics J/K A fundamental thermodynamic property measuring the degree of microscopic disorder, randomness, or thermal energy unavailable for mechanical work in a system. dS = dQ_rev / T, S = kB ln Ω

Entropy in Biological Systems Biophysics & Medical Physics J/K (Entropy) The thermodynamic concept describing how open biological systems maintain high internal structural order by expelling heat and entropy to their environment. dS_system + dS_environment ≥ 0 (Schrödinger: 'Living on Negative Entropy')

Equipartition Theorem Thermodynamics & Statistical Physics J A classical statistical mechanics theorem stating that every independent quadratic degree of freedom contributes ½ kB T to a system's average energy in thermal equilibrium. E_avg = (f / 2) kB T

Equipotential Surface Electromagnetism & Electronics V (Volts) A continuous three-dimensional surface on which every point shares the exact same electric potential. V = constant ⇒ dV = -E · dr = 0

Equivalence Principle Astrophysics, Cosmology & Relativity Fundamental Relativistic Principle The foundational postulate of general relativity asserting that the physical effects of a uniform gravitational field are locally indistinguishable from uniform mechanical acceleration. m_inertial = m_gravitational

Equivalent Dose Biophysics & Medical Physics Sv (Sievert = J/kg) or rem A radiation protection dose quantity weighing absorbed dose by the specific biological effectiveness factor w_R of the radiation type. H = D × w_R (Radiation Weighting Factor w_R)

Error Propagation Mathematical & Computational Physics Uncertainty Units The mathematical evaluation of how uncertainties in measured input variables propagate into the final calculated physical quantity. σ_f² = ∑ (∂f / ∂x_i)² σ_x_i² + 2 ∑ (∂f/∂x_i)(∂f/∂x_j) Cov(x_i, x_j)

Escape Velocity Classical Mechanics m/s The minimum speed required for a ballistic object to escape a massive body's gravitational field without further propulsion. v_esc = √(2 G M / R)

Euler Method Mathematical & Computational Physics First-Order Numerical ODE Integration A basic first-order numerical procedure for solving ordinary differential equations with a given initial value. y_(n+1) = y_n + h f(t_n, y_n)

Euler-Lagrange Equation Mathematical & Computational Physics Calculus of Variations Equation The fundamental partial differential equation of the calculus of variations that a function must satisfy to make a functional stationary. (d / dt) (∂L / ∂q̇_i) - (∂L / ∂q_i) = 0

Terms starting with E