The Physics
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Opus in profectus

Physical Constants

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Physical constants (exact, computed, measured) Sources: exactBIPM; measured, NIST, exception *NASA
symbol name value unit
c  
speed of light in a vacuum
 
299,792,458   m/s
G  
gravitational constant
 
6.67408 × 10−11 Nm2/kg2
h  
planck constant
 
6.62607015
 4.13566770
× 10−34
× 10−15
Js
eVs
hc  
h c
 
1.98644586
1239.841984
× 10−25
 
Jm
eVnm
ℏ = h
h bar
reduced planck constant
dirac constant
1.05457182
 6.58211957
× 10−34
× 10−16
Js
eVs
e  
elementary charge
 
1.602176634 × 10−19 C
ε0 electric constant
permitivitty of free space
vacuum permitivitty
8.854xxxxx × 10−12 C2/Nm2
μ0 magnetic constant
permeability of free space
vacuum permeability
× 10−7 Tm/A
 
NA
 
 
avogadro's constant
 
6.02214076 × 1023 1/mol
k  
boltzmann's constant
 
1.380649 × 10−23 J/K
 
R = NAk
 
 
gas constant
 
8.314462618   J/molK
σ =  5k4
15h3c2
 
stefan-boltzmann constant
 
5.670370374419 × 10−8 W/m2K4
b  
wien displacement constant
 
2.897771955
58.78xxxxx
  mm/K
GHz/K
mu  
atomic mass constant
 
1.660xxxxx
931.4xxxxx
1
× 10−27

 
kg
MeV
u
me  
electron mass
 
9.109xxxxx
0.5109xxxxx
0.0005485xxxxx
× 10−31

 
kg
MeV
u
mp  
proton mass
 
1.672xxxxx
938.2xxxxx
1.007xxxxx
× 10−27

 
kg
MeV
u
mn  
neutron mass
 
1.674xxxxx
939.5xxxxx
1.008xxxxx
× 10−27

 
kg
MeV
u
 
Kcd
 
 
luminous efficacy
 
683    
lm/W
 
g  
standard gravity
 
9.80665   m/s2
atm  
standard atmosphere
 
101,325   Pa
H0
hubble constant*
 
69.3
2.25
 
× 10−18
km/s/Mpc
s−1