Greek Letters in Physics: Complete Symbol Reference
Physics relies heavily on Greek letters to represent fundamental constants, variables, and physical quantities. This guide covers all Greek letters used in classical mechanics, electromagnetism, thermodynamics, quantum mechanics, and modern physics.
Common Greek Letters in Physics
α (Alpha) - Angular Acceleration, Fine Structure Constant
- Angular Acceleration: α = dω/dt (rad/s²)
- Fine Structure Constant: α ≈ 1/137 (dimensionless fundamental constant)
- Alpha Particles: α radiation (helium nuclei)
- Thermal Expansion: α coefficient of linear thermal expansion
β (Beta) - Beta Particles, Velocity Ratio
- Velocity Ratio: β = v/c (velocity as fraction of speed of light)
- Beta Particles: β⁻ (electrons) and β⁺ (positrons) in radioactive decay
- Beta Decay: Nuclear process emitting electrons/positrons
γ (Gamma) - Lorentz Factor, Photon Symbol
- Lorentz Factor: γ = 1/√(1-v²/c²) in special relativity
- Gamma Rays: γ radiation (high-energy photons)
- Heat Capacity Ratio: γ = Cp/Cv (adiabatic index)
- Photons: γ represents photons in particle physics
Δ (Delta) - Change in Quantity
- Change: ΔE (change in energy), Δx (displacement), Δt (time interval)
- Example: Δp = FΔt (impulse-momentum theorem)
ε (Epsilon) - Permittivity, Energy Levels
- Permittivity: ε₀ = 8.854×10⁻¹² F/m (permittivity of free space)
- Relative Permittivity: εᵣ (dielectric constant)
- Energy: Small energy quantities or perturbations
η (Eta) - Efficiency, Viscosity
- Efficiency: η = (useful output)/(total input)
- Dynamic Viscosity: η (Pa·s)
- Example: Carnot efficiency η = 1 - Tc/Th
θ (Theta) - Angles, Phase
- Angles: Angular position, angular displacement
- Phase Angle: In wave equations and AC circuits
- Scattering Angle: In particle collisions
λ (Lambda) - Wavelength, Decay Constant
- Wavelength: λ = c/ν (meters)
- Decay Constant: N(t) = N₀e^(-λt)
- Cosmological Constant: Λ in general relativity
μ (Mu) - Permeability, Coefficient of Friction, Muon
- Magnetic Permeability: μ₀ = 4π×10⁻⁷ H/m
- Coefficient of Friction: μ = F_friction/F_normal
- Muon: μ⁻ (unstable elementary particle)
- Reduced Mass: μ = m₁m₂/(m₁+m₂)
ν (Nu) - Frequency, Neutrino
- Frequency: ν = 1/T (Hz, cycles per second)
- Energy Relation: E = hν (Planck's equation)
- Neutrinos: ν_e, ν_μ, ν_τ (electron, muon, tau neutrinos)
- Kinematic Viscosity: ν = μ/ρ
π (Pi) - Mathematical Constant in Physics
- Circular Motion: Circumference = 2πr
- Angular Velocity: ω = 2πf
- Constants: Appears in many physical constants
ρ (Rho) - Density, Resistivity, Charge Density
- Mass Density: ρ = m/V (kg/m³)
- Electrical Resistivity: ρ (Ω·m)
- Charge Density: ρ (C/m³)
σ (Sigma) - Surface Charge Density, Stefan-Boltzmann Constant
- Surface Charge: σ (C/m²)
- Stefan-Boltzmann: σ = 5.67×10⁻⁸ W/(m²·K⁴)
- Cross Section: σ in particle physics (area)
Σ (Sigma) - Summation
- Sum of Forces: ΣF = ma (Newton's second law)
- Total Energy: E_total = ΣE_i
τ (Tau) - Torque, Time Constant, Tau Lepton
- Torque: τ = r × F (N·m)
- Time Constant: τ = RC in circuits, τ = L/R
- Tau Lepton: τ⁻ (heavy lepton)
- Shear Stress: τ (Pa)
Φ (Phi) - Magnetic Flux, Electric Potential
- Magnetic Flux: Φ_B = B·A (Weber, Wb)
- Electric Potential: Φ or V (Volts)
- Work Function: φ (minimum energy to remove electron)
φ (Phi) - Angles, Phase, Golden Ratio
- Phase Angle: In spherical coordinates
- Azimuthal Angle: φ in spherical/cylindrical coordinates
χ (Chi) - Electric Susceptibility
- Electric Susceptibility: χ_e relates polarization to field
- Magnetic Susceptibility: χ_m
ψ (Psi) - Wave Function
- Quantum Wave Function: ψ(x,t) in Schrödinger equation
- Probability: |ψ|² gives probability density
- Stream Function: ψ in fluid dynamics
ω (Omega) - Angular Frequency
- Angular Velocity: ω = dθ/dt (rad/s)
- Angular Frequency: ω = 2πf
- Simple Harmonic Motion: x = A·cos(ωt + φ)
Ω (Omega) - Ohm, Solid Angle
- Ohm: Ω unit of electrical resistance
- Solid Angle: Ω (steradians)
Greek Letters by Physics Field
| Field | Common Letters | Typical Uses |
|---|---|---|
| Classical Mechanics | α, ω, τ, θ | Angular quantities, angles, torque |
| Electromagnetism | ε, μ, ρ, σ, Φ | Permittivity, permeability, charge, flux |
| Thermodynamics | η, γ, σ, Δ | Efficiency, heat ratio, radiation |
| Quantum Mechanics | ψ, λ, ν | Wave function, wavelength, frequency |
| Special Relativity | γ, β | Lorentz factor, velocity ratio |
| Nuclear Physics | α, β, γ, λ | Radiation, decay constant |
| Particle Physics | γ, μ, τ, ν | Photons, muons, tau, neutrinos |
Fundamental Physical Constants with Greek Letters
- ε₀: Permittivity of free space = 8.854×10⁻¹² F/m
- μ₀: Permeability of free space = 4π×10⁻⁷ H/m
- σ: Stefan-Boltzmann constant = 5.67×10⁻⁸ W/(m²·K⁴)
- α: Fine structure constant ≈ 1/137
- Φ₀: Magnetic flux quantum = 2.07×10⁻¹⁵ Wb