In Science!

                 

                In science, a physical constant is a physical quantity whose numerical value is fixed. There are many constants used in science, some of the most famous being: Planck's constant, the gravitational acceleration and Avogadro's number. Constants can be of many kinds, some, like the Planck length is a fundamental physical distance, others like the speed of ligt meaning the speed limit in our known universe. Is it? 

Below is a list of physical constants:       

Constantă	Simbol	Valoare	Ref.
speed of light in vacuum	c	299.792.458 m·s-1 (prin def.)	a
vacuum permeability	μ0	4π × 10-7 N A-2 (prin def.)	a
		12.566 370 614... × 10-7 N A-2	a
permittivity of vacuum	ε0 = 1/(μ0c2)	8.854 187 817 ... × 10-12 F·m-1	a
characteristic impedance of vacuum	Z0 = μ0c	376.730 313 461... Ω (prin def.)	a
gravitational constant	G	6.672 59(85) × 10-11 m3·kg-1·s-2	?
Planck's constant	h	6.626 068 76(52) × 10-34 J·s	a
Dirac's constant	= h / (2π)	1.054 571 596(82) × 10-34 J·s	a
Planck mass	mp = (c / G)1/2	2.1767(16) × 10-8 kg	a
Planck length	lp= (G / c3) 1/2	1.6160(12) × 10-35 m	a
Planck time	tp = (G / c5)1/2	5.3906(40) × 10-44 s	a
elementary charge	e	1.602 176 462(63) × 10-19 C	a
rest mass of the electron	me	9.109 381 88(72) × 10-31 kg	a
rest mass of the proton	mp	1.672 621 58(13) × 10-27 kg	a
rest mass of the neutron	mn	1.674 927 16(13) × 10-27 kg	a
atomic mass unit	mu = 1 u	1.660 538 73(13) × 10-27 kg	a
Avogadro's number	L, NA	6.022 141 99(47) × 1023	a
Boltzmann's constant	k	1.380 6503(24) × 10-23 J·K-1	a
Faraday's constant	F	9.648 534 15(39) × 104 C·mol-1	a
ideal gas constant	R	8.314 472(15) J·K-1·mol-1	a
zero on Celsius scale		273.15 K (prin def.)	?
molar volume of ideal gas, p = 1 bar, θ = 00C		22.710 981(40) L·mol-1	a
standard atmosphere	atm	101 325 Pa (prin def.)	a
fine structure constant	α = μ0e2c / (2h)	7.297 352 533(27) × 10-3	a
	α-1	137.035 999 76(50)	a
Bohr radius	a0	5.291 772 083(19) × 10-11 m	a
Hartree energy	Eh	4.359 743 81(34) × 10-18 J	a
Rydberg's constant	R∞	1.097 373 156 8549(83) × 107 m-1	a
Bohr magneton	μB	9.274 008 99(37) × 10-24 J·T-1	a
magnetic moment of the electron	μe	-9.284 763 62(37) × 10-24 J·T-1	a
Lande's g factor for free electron	ge	2.02.319.304 386(20)	?
nuclear magneton	μN	5.050 786 6(17) × 10-27 J·T-1	?
magnetic moment of the proton	μp	1.410 607 61(47) × 10-26 J·T-1	?
giromagnetic ratio of the proton	γp	2.675 221 28(81) × 108 s-1·T-1	?
magnetic moment of protons in H20​​, μ'p	μ'p / μB	1.520 993 129(17) × 10-3	?
proton resonance frequency per field H20	γ'p / (2π)	42.576 375 (13) M·Hz·T-1	?
Stefan-Boltzmann constant	σ	5.670 400(40) × 10-8 W·m-2·K-4	a
first radiative constant	c1	3.741 774 9(22) × 10-16 W·m2	?
second radiative constant	c2	1.438 769 (12) × 10-2 m·K	?
standard acceleration of free fall	gn	9.80665 m·s-2 (prin def.)	?

       Some "constants" are in fact artificial system of units used, for example, mks or cgs. In natural units, some of these so-called physical constants are found to be only simple conversion factors.
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