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# Some Physical Constants

## C.1. Mechanical and thermodynamic constants

 Speed of light in a vacuum (exact value) c = 299,792,458 × 108 m/s Gravitational constant G = 6.67259 (85) × 10−11 N.m2/kg2 Standard acceleration of free fall g = 9.80665 m/s2 Sideral year 365.2564 days Normal pressure po = 1 At = l.01325 × 105 N/m2 Normal temperature To = 273.16 K Mechanical equivalent of the calorie J = 4.1855 (4) J/Cal Mass density of dry air (STP) ρo = 1.2929 kg/m3 Speed of sound in air (STP) vs = 331.36 m/s Molar volume of ideal gases (STP) Vm = 2.241383 (70) × 10−2 m3/mole Avogadro number No = 6.0221367 (36) × 1023 mole−1 Boltzmann constant K = 1.380658 (12) × 10−23 J/K Gas constant R = 8.314510 (70) J/K.mole Acoustic impedance of air (STP) Za = 428 N.s/m3
 Threshold of hearing sound intensity 10−2 W/m2 Stefan-Boltzmann constant σ = 5.67051 (7) × 10−8 J/m2.s.K4 Mass density of mercury 13,595.5 kg/m3

Table C.1. Mechanical and thermodynamic quantities. Standard g means at sea level and at latitude of 45°. STP means standard temperature (0 °C) and pressure (760 mm Hg)

## C.2. Electromagnetic and atomic constants

 Elementary charge e = 1.60217733 (49) × 10−19 C Electron-volt eV = 1.6021892 (46) × 10−19 J Planck constant h = 6.626075 (40) × 10−34 J.s   = 4.135669 (11) 10−15 eV.s Reduced Plank constant ħ = h/2π = 1.054572 66 (63) × 10−34 ...

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