Units & Dimensions Physical Constants

 Units & Dimensions 

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-1One 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 (μ0) = 4π × 10-7 Hm-1

• Permittivity of free space (ε0) = 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