Electromagnetism & Electronics — 67 Terms Defined

Ampere's Circuital Law Electromagnetism & Electronics T·m (Tesla-meters) Maxwell's fourth equation (in magnetostatics) relating the integrated magnetic field around a closed Amperian loop to net electric current passing through the loop. ∮ B · dl = μ₀ I_enclosed

Biot-Savart Law Electromagnetism & Electronics T (Tesla) An equation describing the magnetic field vector generated at a point in space by a steady differential electric current element. dB = (μ₀ / 4π) (I dl × r̂) / r²

Bipolar Junction Transistor (BJT) Electromagnetism & Electronics A (Current) A three-terminal active semiconductor device (NPN or PNP) in which a small base current controls a much larger collector-emitter current. I_E = I_B + I_C, I_C = β I_B

Capacitance Electromagnetism & Electronics F (Farads = C/V) The ratio of the electric charge stored on a conductor or capacitor plate to the potential difference across it. C = q / V = ε A / d

Capacitive Reactance Electromagnetism & Electronics Ω (Ohms) The opposition offered by a capacitor to alternating current flow, inversely proportional to AC frequency and capacitance. X_C = 1 / (2π f C) = 1 / (ω C)

Coulomb's Law Electromagnetism & Electronics N (Newtons) An inverse-square law stating that the electrostatic force between two stationary point charges is directly proportional to the product of their charges and inversely proportional to the square of their… F = k_e |q₁ q₂| / r² = (1 / (4π ε₀)) |q₁ q₂| / r²

Cyclotron Electromagnetism & Electronics Hz (Frequency), J or MeV (Kinetic Energy) A particle accelerator in which charged particles orbit spirally in a constant magnetic field while high-frequency AC electric fields accelerate them twice per turn. f_c = (q B) / (2π m), KE_max = (q² B² R²) / (2 m)

Diamagnetism Electromagnetism & Electronics Dimensionless A universal weak magnetic property of matter where applied magnetic fields induce opposing atomic orbital currents that weakly repel the material. χ_m < 0 (χ_m ~ -10⁻⁵)

Displacement Current Electromagnetism & Electronics A (Amperes) A fictitious effective current term introduced by Maxwell to account for magnetic field generation by time-varying electric fields. I_d = ε₀ (dΦ_E / dt)

Eddy Currents Electromagnetism & Electronics W (Watts) Loops of electric current induced within solid bulk conductors by a changing magnetic field according to Faraday's law. P_eddy ∝ f² B_max² t²

Electric Charge Electromagnetism & Electronics C (Coulombs) A fundamental intrinsic physical property of subatomic particles that causes matter to experience an electrostatic force when placed in an electromagnetic field. q = n e, e = 1.602 × 10⁻¹⁹ C

Electric Current Electromagnetism & Electronics A (Amperes = C/s) The rate of net flow of electric charge through a cross-sectional area of a conductor per unit time. I = dq/dt = n q v_d A

Electric Dipole Electromagnetism & Electronics C·m (Coulomb-meters) A system of two equal and opposite electric charges (+q and -q) separated by a small distance d. p = q d, V = (1 / (4π ε₀)) (p cos θ / r²)

Electric Dipole Moment Electromagnetism & Electronics C·m (or Debye) A vector quantity measuring the strength and orientation of an electric dipole, pointing from the negative charge toward the positive charge. p = q d, τ = p × E, U = -p · E

Electric Field Electromagnetism & Electronics N/C (or V/m) A vector field surrounding an electric charge that exerts an electrostatic force on any other charge placed within the field. E = F / q = -∇V = (1 / (4π ε₀)) q / r² r̂

Electric Potential Electromagnetism & Electronics V (Volts = J/C) 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

Electric Power Electromagnetism & Electronics W (Watts = J/s) 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

Electric Susceptibility Electromagnetism & Electronics Dimensionless A dimensionless material property measuring the degree of electric polarization induced in a dielectric material by an applied electric field. P = ε₀ χ_e E, ε_r = 1 + χ_e

Electrical Conductivity Electromagnetism & Electronics S/m (Siemens per meter) An intrinsic material property measuring its ability to conduct electric current, defined as the reciprocal of electrical resistivity. σ = 1 / ρ = J / E

Electrical Resistance Electromagnetism & Electronics Ω (Ohms = V/A) A measure of the opposition that a circuit element or material presents to the flow of electric current. R = V / I = ρ L / A

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

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

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