Electromagnetism & Electronics

Ampere's Circuital Law

Maxwell's fourth equation (in magnetostatics) relating the integrated magnetic field around a closed Amperian loop to net electric current…

∮ B · dl = μ₀ I_enclosed T·m (Tesla-meters)

Biot-Savart Law

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 T (Tesla)

Electromagnetism & Electronics

Bipolar Junction Transistor (BJT)

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 A (Current)

Electromagnetism & Electronics

Capacitance

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 F (Farads = C/V)

Electromagnetism & Electronics

Capacitive Reactance

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) Ω (Ohms)

Electromagnetism & Electronics

Coulomb's Law

An inverse-square law stating that the electrostatic force between two stationary point charges is directly proportional to the product of…

F = k_e |q₁ q₂| / r² = (1 / (4π ε₀)) |q₁ q₂| / r² N (Newtons)

Electromagnetism & Electronics

Cyclotron

A particle accelerator in which charged particles orbit spirally in a constant magnetic field while high-frequency AC electric fields…

f_c = (q B) / (2π m), KE_max = (q² B² R²) / (2 m) Hz (Frequency), J or MeV (Kinetic Energy)

Electromagnetism & Electronics

Diamagnetism

A universal weak magnetic property of matter where applied magnetic fields induce opposing atomic orbital currents that weakly repel the…

χ_m < 0 (χ_m ~ -10⁻⁵) Dimensionless

Electromagnetism & Electronics

Displacement Current

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) A (Amperes)

Electromagnetism & Electronics

Eddy Currents

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 W (Watts)

Electromagnetism & Electronics

Electric Charge

A fundamental intrinsic physical property of subatomic particles that causes matter to experience an electrostatic force when placed in an…

q = n e, e = 1.602 × 10⁻¹⁹ C C (Coulombs)

Electromagnetism & Electronics

Electric Current

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 A (Amperes = C/s)

Electromagnetism & Electronics

Electric Dipole

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) C·m (Coulomb-meters)

Electromagnetism & Electronics

Electric Dipole Moment

A vector quantity measuring the strength and orientation of an electric dipole, pointing from the negative charge toward the positive…

p = q d, τ = p × E, U = -p · E C·m (or Debye)

Electromagnetism & Electronics

Electric Field

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 N/C (or V/m)

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)

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)

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)