## Some important conversions and physical constants

Some Important Conversions

- 1 bar = 106 dyne/cm2 = 105 Nm-2 = 105 pascal
- 76 cm of Hg = 1.013×106 dyne/cm2 = 1.013×105 pascal = 1.013 bar.
- 1 toricelli or torr = 1 mm of Hg = 1.333×103 dyne/cm2 = 1.333 millibar.
- 1 kmph = 5/18 ms-1
- 1 dyne = 10-5 N,
- 1 H.P = 746 watt
- 1 kilowatt hour = 36×105 J
- 1 kgwt = g newton
- 1 calorie = 4.2 joule
- 1 electron volt = 1.602×10-19 joule
- 1 erg = 10-7 joule

Some Important Physical Constants

- Velocity of light in vacuum (c) = 3 × 108 ms-1
- Velocity of sound in air at STP = 331 ms-1
- Acceleration due to gravity (g) = 9.81 ms-2
- Avogadro number (N) = 6.023 × 1023/mol
- Density of water at 4oC = 1000 kgm-3 or 1 g/cc.
- Absolute zero = -273.15oC or 0 K
- Atomic mass unit = 1.66 × 10-27 kg
- Quantum of charge (e) = 1.602 × 10-19 C
- Stefan’s constant = 5.67 × 10–8 W/m2/K4
- Boltzmann’s constant (K) = 1.381 × 10-23 JK-1
- One atmosphere = 76 cm Hg = 1.013 × 105 Pa
- Mechanical equivalent of heat (J) = 4.186 J/cal
- Planck’s constant (h) = 6.626 × 10-34 Js
- Universal gas constant (R) = 8.314 J/mol–K
- Permeability of free space () = 4π × 10-7 Hm-1
- Permittivity of free space () = 8.854 × 10-12 Fm-1
- The density of air at S.T.P. = 1.293 kg m-3
- Universal gravitational constant = 6.67 × 10-11 Nm2kg-2