# About the Common uses in Physics

While these are indeed common usages, it should be pointed out that there are many other usages and that other letters are used for the same purpose. The reason is quite simple: there are only so many symbols in the Greek and Latin alphabets, and scientists and mathematicians generally do not use symbols from other languages. It is a common trap to associate a symbol exclusively with some particular meaning, rather than learning and understanding the physics and relations behind it.

Greek Alphabet
Capital Lower case Name Common use in Physics
${\displaystyle \mathrm {A} }$  ${\displaystyle \alpha }$  alpha Angular acceleration
Linear expansion
Coefficient
Alpha particle (helium nucleus)
Fine Structure Constant
${\displaystyle \mathrm {B} }$  ${\displaystyle \beta }$  beta Beta particle — high energy electron
Sound intensity
${\displaystyle \Gamma }$  ${\displaystyle \gamma }$  gamma Gamma ray (high energy EM wave)
Ratio of heat capacities (in an ideal gas)
Relativistic correction factor

Shear strain

${\displaystyle \Delta }$  ${\displaystyle \delta }$  delta Δ="Change in"
δ="Infinitesimal change in (), also used to denote the Dirac delta function (reference needed)"
${\displaystyle \mathrm {E} }$  ${\displaystyle \epsilon }$  epsilon Emissivity
Strain (Direct e.g. tensile or compression)
Permittivity
EMF
${\displaystyle \mathrm {Z} }$  ${\displaystyle \zeta }$  zeta (no common use)
${\displaystyle \mathrm {H} }$  ${\displaystyle \eta }$  eta Viscosity
Energy efficiency
${\displaystyle \Theta }$  ${\displaystyle \theta }$  theta Angle (°, rad)
Temperature
${\displaystyle \mathrm {I} }$  ${\displaystyle \iota }$  iota The lower case ${\displaystyle \iota \;}$  is rarely used, while ${\displaystyle \mathrm {I} }$  is sometimes used for the identity matrix or the moment of inertia. Note that ${\displaystyle \iota }$  is not to be confused with the Roman character ${\displaystyle i}$  (which has a dot and is much more widely used in mathematics and physics).
${\displaystyle \mathrm {K} }$  ${\displaystyle \kappa }$  kappa Spring constant
Dielectric constant
${\displaystyle \Lambda }$  ${\displaystyle \lambda }$  lambda Wavelength
Thermal conductivity
Constant
Eigenvalue of a matrix
Linear density
${\displaystyle \mathrm {M} }$  ${\displaystyle \mu }$  mu Coefficient of friction
Electrical mobility
Reduced mass
Permeability
${\displaystyle \mathrm {N} }$  ${\displaystyle \nu }$  nu Frequency
${\displaystyle \Xi }$  ${\displaystyle \xi }$  xi Damping cofficient
${\displaystyle \mathrm {O} }$  ${\displaystyle \mathrm {o} }$  omicron (no common use)
${\displaystyle \Pi }$  ${\displaystyle \pi }$  pi Product symbol ${\displaystyle \Pi }$
Circle number ${\displaystyle \pi :=3.14159...}$
${\displaystyle \mathrm {P} }$  ${\displaystyle \rho }$  rho Volume density
Resistivity
${\displaystyle \Sigma }$  ${\displaystyle \sigma }$  sigma Sum symbol
Boltzmann constant
Electrical conductivity
Uncertainty
Stress (Direct e.g. tensile, compression)
Surface density
${\displaystyle \mathrm {T} }$  ${\displaystyle \tau }$  tau Torque
Tau particle (a lepton)
Time constant

Shear stress

${\displaystyle \Upsilon }$  ${\displaystyle \upsilon }$  upsilon mass to light ratio
${\displaystyle \Phi }$  ${\displaystyle \phi }$  phi Magnetic/electric flux
${\displaystyle \mathrm {X} }$  ${\displaystyle \chi }$  chi Rabi frequency (lasers)
${\displaystyle \Psi }$  ${\displaystyle \psi }$  psi Wave function
${\displaystyle \Omega }$  ${\displaystyle \omega }$  omega Ohms (unit of electrical resistance)