Home > Centimetre gram second system of units

1 Electromagnetic Units

While for most units the difference between cgs and SI is a mere power of 10, the differences in electromagnetic units are considerable; so much so that formulas for physical laws need to be changed depending on what system of units one uses. In SI, electric current is defined via the magnetic force it exerts and charge is then defined as current multiplied with time. In one variant of the cgs system, esu, or electrostatic units, charge is defined via the force it exerts on other charges, and current is then defined as charge per time. One consequence of this approach is that Coulomb's law does not contain a constant of proportionality.

There are actually about half a dozen systems of electromagnetic units in use, most based on the cgs system. These include emu, or electromagnetic units (chosen such that the Biot-Savart Law has no constant of proportionality), Gaussian, and Heaviside-Lorentz units. Further complicating matters is the fact that some physicists and engineers use hybrid units, such as volts per centimetre for electric field.

2 Units

The units of cgs (specifically esu) are as follows:

• length: centimetre 1 cm = 0.01 m
• massMass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. It is a central concept of classical mechanics and related subjects. Strictly speaking, there are two different quantities called mass Inertial mass: gramFor other meanings of gram see gram (disambiguation). The gram (also spelt gramme is a unit of measurement of mass, and is defined in the SI system of units as one thousandth of a kilogram. See 1 E -3 kg for comparisons with other masses. The symbol for g 1 g = 0.001 kg
• timeFor alternate uses of "time", see Time (disambiguation). Time quantifies or measures the interval between events, or the duration of events. Time has long been perceived as a dimension in which each event has a definite (but not necessarily unique) positi: secondThis article is about the unit of time. See second (disambiguation) for other uses The second (symbol s is a unit for time, and one of seven SI base units. It is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transi
• force: dyneIn physics, the dyne is a unit of force specified in the centimetre-gram-second (cgs) system of units, symbol "dyn". One dyne is equal to exactly 10-5 newtons. Further, the dyne can be defined as "the force required to accelerate a mass of one gram at a r = g·cm/s² = 10^-5 NThis article is about the SI unit of force. For other uses see Newton (disambiguation In physics, the newton (symbol: N) is the SI unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics. It was adopted by the General
• energy: erg = g·cm²/s² = 10^-7 J
• power: g·cm²/s³ = 10^-7 W
• pressure: barye = g/cm·s² = 0.1 Pa
• viscosity: poise = g/cm·s = 0.1 Pa·s
• charge: esu, franklin or statcoulomb = √ (g·cm³/s²) = 3.336 × 10^-10 C
• electric potential: statvolt = erg/esu = 299.8 V
• electric field: statvolt/cm = dyne/esu
• magnetic field: 1 gauss (not used) = 1 oersted = 1 statvolt/cm = 1 dyn/esu = 10^-4 T
• magnetic flux: 1 maxwell = 1 gauss·cm² = 10^-8 Wb
• magnetic induction: 1 gauss = 1 maxwell/cm²
• resistance: s/cm
• resistivity: s
• capacitance: cm = 1.113 × 10^-12 F
• inductance: s²/cm = 8.988 × 10¹¹ H

The mantissas 2998, 3336, 1113, and 8988 are derived from the speed of light and are more precisely 299792458, 333564095198152, 1112650056, and 89875517873681764.

A centimetre of capacitance is the capacitance between a sphere of radius 1 cm in vacuum and infinity. The capacitance between two spheres of radii R and r is