Useful Constants
This is a table of some common constants and their symbols. These are typically named after whichever physics guru invented/discovered/first used/etc them. Symbols are often repeated in physics due to the limited nature of the Pool of Physics Symbols. Symbols that are used for variables are also used for constants. You should be able to tell which one you need from the context it is being used in. For example: the symbol "h" is often used to describe height (a variable), but is also the symbols for Planck's constant (a constant.) In an equation, whether I use a height measurement, such as 3 meters, for "h" or I use the value of Planck's constant for "h" will depend on whether I'm dealing with classical physics or modern physics. So pay attention to the context of the problem and you shouldn't encounter much difficulty. All of the constants on this page were adopted from a list my Modern Physics professor supplied to me at the beginning of the semester. Many thanks to whomever originally compiled the list - it has been invaluable during the course of my education.
| Name | Symbol | Value | Commonly Used In |
| Atomic mass unit | u | 1 u = (1/12) mol(12C
atoms)
= 1.66 x 10-27 kg = 931.5 MeV/c2 |
chemistry, atomic physics, modern physics, nuclear physics |
| Avogadro's constant | NA | = 6.022 x 1023 /mol | chemistry, atomic physics, modern physics, nuclear physics |
| Bohr magneton | μb | = eħ/(2me)
= 5.79 x 10-5 eV/T = 9.27 x 10-24 J/T (or A·m2) |
atomic physics, modern physics, nuclear physics |
| Bohr radius | aB or r0 | = ħ2/(ke2me)
= 5.29 x 10-11 m |
atomic physics, modern physics, nuclear physics |
| Boltzmann's constant | kB | = 8.62 x 10-5 eV/K
= 1.38 x 10-23 J/K |
modern physics |
| Coulomb force constant | k | = 1/(4πε0)
= μ0c2/(4π)
= 8.99 x 109 N·m2/c2 |
electricity and magnetism, classical physics, modern physics |
| Electron Compton wavelength | λc | = h/(mec)
= 2.43 x 10-12 m |
modern physics, nuclear physics, quantum mechanics, electricity & magnetism |
| Electron volt | eV | 1 eV = 1.60 x 10-19 J | All fields of physics |
| Elementary charge | e | = 1.60 x 10-19 C | All fields of physics |
| Fine-structure constant | α |
=ke2/(ħc)
=7.30 x 10-3 ≈ 1/137 |
modern physics. optics |
| Gas constant | R | = 8.31 J/(mol K)
= 0.0821 liter·atm/(mol·K) |
classical physics, chemistry, fluid dynamics, thermodynamics |
| Gravitational constant | G | = 6.67 x 10-11 N·m2/kg2 | astrophysics, classical physics |
| Mass of electron | me | = 5.49 x 10-4 u
= 9.11 x 10-31 kg = 0.511 MeV/c2 |
chemistry, atomic physics, modern physics, nuclear physics, quantum mechanics, electricity & magnetism |
| Mass of neutron | mn | = 1.009 u
= 1.675 x 10-27 kg = 938.3 MeV/c2 |
chemistry, atomic physics, modern physics, nuclear physics |
| Mass of proton | mp | = 1.007 u
= 1.673 x 10-27 kg = 939.6 MeV/c2 |
chemistry, atomic physics, modern physics, nuclear physics |
| Nuclear magneton | μN | = eħ/(2mp)
= 3.15 x 10-8 eV/T = 5.05 x 10-27 J/T |
chemistry, atomic physics, modern physics, nuclear physics |
| Permeability of space | μ0 | = 4π
x 10-7 N/A2
= 1.28 x 10-6 N/A2 |
atomic physics, modern physics, nuclear physics, quantum mechanics, electricity & magnetism, astrophysics, classical physics |
| Permittivity of free space | ε0 | = 1/(μ0c2)
= 8.85 x 10-12 c2/(N·m2) |
atomic physics, modern physics, nuclear physics, quantum mechanics, electricity & magnetism, astrophysics, classical physics |
| Planck's constant | h | h = 6.63 x 10-34 J·s
= 4.14 x 10-15 eV·s ħ = h/2π = 1.05 x 10-34 J·s = 6.58 x 10-16 eV·s |
atomic physics, modern physics, nuclear physics, quantum mechanics, electricity & magnetism |
| Rydberg constant | R | = mek2e4/(4πcħ3)
= 1.10 x 10-2 /nm |
atomic physics, modern physics, nuclear physics, quantum mechanics, electricity & magnetism |
| Rydberg energy | ER | = hcR = mek2e4/(2ħ2)
= 13.6 eV |
atomic physics, modern physics, nuclear physics, quantum mechanics, electricity & magnetism |
| Speed of light in a vacuum | c | = 3.00 x 108 m/s | relativity, modern physics, quantum mechanics, electricity and magnetism. |
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