Constants

This page lists various constants used in physics and some useful conversions.

Physical constants

The number in brackets represents the uncertainty in the constant, so that $\text{[math]}$ has an uncertainty of $\text{[math]}$ .

Name	Symbol	Value	Meaning	Used in	Exact
Planck's constant	$\text{[math]}$	$\text{[math]}$	It relates the frequency of a photon to its energy	Quantum mechanics	Inexact^[1]
Speed of light	$\text{[math]}$	$\text{[math]}$	This is the speed of light in a vacuum	Most of physics, such as optics and relativity	Exact^[2]
Permittivity of free space	$\text{[math]}$	$\text{[math]}$	Related to the strength of an electric field produced by a charge	Electromagnetism	Exact^[3]
Permeability of free space	$\text{[math]}$	$\text{[math]}$	Related to the strength of [[magnetic field]s produced by a current	Electromagnetism	Exact^[4]
Elementary charge	$\text{[math]}$	$\text{[math]}$	The magnitude of the electric charge on an electron	Determines the strength of electric and magnetic fields produced by protons, electrons etc	Inexact^[5]
Avogadro's number	$\text{[math]}$	$\text{[math]}$	The number of constituents in 1 mole of something	Chemistry, statistical mechanics, thermodynamics	Inexact^[6]
Ideal gas constant	$\text{[math]}$	$\text{[math]}$	Relates the pressure, volume, temperature and number of moles of an ideal gas	Thermodynamics	Inexact^[7]
Faraday Constant	$\text{[math]}$	$\text{[math]}$	The electric charge on one mole of electrons (Avogadro's number times elementary charge)	Chemistry, physics	Inexact^[8]
Gravitational constant	$\text{[math]}$	$\text{[math]}$	Constant related to the strength of Newtonian gravity	Newtonian gravity	Inexact^[9]
Boltzmann constant	$\text{[math]}$	$\text{[math]}$	Thermodynamics		Inexact^[10]
Reduced Planck's constant	$\text{[math]}$	$\text{[math]}$	Quantum mechanics	It is Planck's constant divided by $\text{[math]}$ .	Inexact^[11]
Wien displacement constant	$\text{[math]}$	$\text{[math]}$	Relates the temperature of a black body to the peak in its spectrum		Inexact^[12]
Standard acceleration due to gravity	$\text{[math]}$	$\text{[math]}$	This is the acceleration of any object near to the earth's surface when gravity is the only force acting (ie, no air resistance).	Mechanics	Exact^[13]
Proton mass	$\text{[math]}$	$\text{[math]}$	Rest mass of a proton		Inexact^[14]
Neutron mass	$\text{[math]}$	$\text{[math]}$	Rest mass of a neutron		Inexact^[15]
Electron mass	$\text{[math]}$	$\text{[math]}$	Rest mass of an electron		Inexact^[16]