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Electromagnetism & Electronics

Electric Potential

The electric potential energy per unit charge at a point in an electric field relative to a chosen reference point.

V = U / q = (1 / (4π ε₀)) q / r V (Volts = J/C) Electromagnetism & Electronics

Electric Power

The rate at which electrical energy is transferred, converted, or dissipated by an electric circuit component per unit time.

P = V I = I² R = V² / R W (Watts = J/s) Electromagnetism & Electronics

Electric Susceptibility

A dimensionless material property measuring the degree of electric polarization induced in a dielectric material by an applied electric…

P = ε₀ χ_e E, ε_r = 1 + χ_e Dimensionless Electromagnetism & Electronics

Electrical Conductivity

An intrinsic material property measuring its ability to conduct electric current, defined as the reciprocal of electrical resistivity.

σ = 1 / ρ = J / E S/m (Siemens per meter) Electromagnetism & Electronics

Electrical Resistance

A measure of the opposition that a circuit element or material presents to the flow of electric current.

R = V / I = ρ L / A Ω (Ohms = V/A) Electromagnetism & Electronics

Electrical Resistivity

An intrinsic material property quantifying how strongly a material opposes the flow of electric current.

ρ = R A / L = 1 / σ Ω·m (Ohm-meters) Biophysics & Medical Physics

Electro-osmosis

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) m/s (Electro-osmotic Velocity) Biophysics & Medical Physics

Electrocardiography (ECG)

A non-invasive diagnostic technique recording the spatial bioelectric potential changes produced by heart muscle depolarization and…

Cardiac Dipole Vector P(t), Einthoven's Triangle Lead Vectors mV (Amplitude ~1 mV) & bpm (Heart Rate) Biophysics & Medical Physics

Electroencephalography (EEG)

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) μV (Microvolts ~10–100 μV) & Hz Electromagnetism & Electronics

Electromagnetic Spectrum

The continuous range of all frequencies and wavelengths of electromagnetic radiation, ordered from low-frequency radio waves to…

c = f λ, E = h f Hz (Frequency), m (Wavelength) Electromagnetism & Electronics

Electromagnetic Waves

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 m/s (Velocity) Quantum & Atomic Physics

Electron Spin

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 J·s (Spin Angular Momentum) Biophysics & Medical Physics

Electroporation

A biophysical technique applying short, high-voltage electric field pulses to cells to temporarily increase cell membrane permeability by…

Critical Transmembrane Breakdown Voltage V_c ≈ 0.5–1.0 V kV/cm (Electric Field Strength) Foundations of Physics

Elementary Charge

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 C Thermodynamics & Statistical Physics

Emissivity

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) Dimensionless Waves, Oscillations & Acoustics

End Correction

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) m Foundations of Physics

Energy

The quantitative property that must be transferred to a physical system to perform work on it, or to heat it.

E = mc² J Nuclear & Particle Physics

Enriched Uranium

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%) Weight Percent (% ²³⁵U) Thermodynamics & Statistical Physics

Enthalpy

A thermodynamic potential defined as internal energy plus the product of pressure and volume, representing total heat content under…

H = U + P V, ΔH = Q_p J Thermodynamics & Statistical Physics

Entropy

A fundamental thermodynamic property measuring the degree of microscopic disorder, randomness, or thermal energy unavailable for mechanical…

dS = dQ_rev / T, S = kB ln Ω J/K Biophysics & Medical Physics

Entropy in Biological Systems

The thermodynamic concept describing how open biological systems maintain high internal structural order by expelling heat and entropy to…

dS_system + dS_environment ≥ 0 (Schrödinger: 'Living on Negative Entropy') J/K (Entropy) Thermodynamics & Statistical Physics

Equipartition Theorem

A classical statistical mechanics theorem stating that every independent quadratic degree of freedom contributes ½ kB T to a system's…

E_avg = (f / 2) kB T J Electromagnetism & Electronics

Equipotential Surface

A continuous three-dimensional surface on which every point shares the exact same electric potential.

V = constant ⇒ dV = -E · dr = 0 V (Volts) Astrophysics, Cosmology & Relativity

Equivalence Principle

The foundational postulate of general relativity asserting that the physical effects of a uniform gravitational field are locally…

m_inertial = m_gravitational Fundamental Relativistic Principle