The statcoulomb (statC) or franklin (Fr) or electrostatic unit of charge (esu) is the physical unit for electrical charge used in the centimetre-gram-second (cgs) electrostatic system of units. The SI system of units uses the coulomb (C) instead. The conversion is The definition, agreement and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. ... Electric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. ... This article or section is in need of attention from an expert on the subject. ... Cover of brochure The International System of Units. ... The coulomb (symbol: C) is the SI unit of electric charge. ...

1 statC = 0.1 Am/c ≈ 3.33564×10⁻¹⁰ C

The conversion factor (≈ 3.33564×10⁻¹⁰) is equal to 10 divided by the numerical value of the speed of light, c, expressed in cm/s. The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation in a vacuum, not just visible light. ...

In the electrostatic cgs system, electrical charge is a fundamental quantity defined via the electrostatic force (see below); in the SI system, electrical current is fundamental and defined via the electromagnetic force while electrical charge is a derived quantity. The electrostatic system derives the electric charge from Coulomb's law and takes the permittivity as a dimensionless quantity whose value in a vacuum is 1/(4π). Also the use of the permeability of vacuum, , is avoided, having the consequence that the speed of light appears explicitly in some of the equations interrelating quantities in this system. Coulombs torsion balance In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... Permeability has several meanings: In electromagnetism, permeability is the degree of magnetisation of a material in response to a magnetic field. ...

The statcoulomb is defined as follows: if two objects each carry a charge of 1 statC and are 1 cm apart, they will repel each other with a force of 1 dyne. As a result, in the electrostatic cgs system, Coulomb's law describing the force F between two charges q₁ and q₂ a distance r apart takes the simple form: In 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. ...

Note that in order for the Coulomb's law formula to work using the electrostatic cgs system, the dimension of electrical charge must be [mass]^1/2 [length]^3/2 [time]^-1. This is different from the dimension of coulombs which accounts for the fact that the factor k mentioned below is not dimensionless. Dimensional analysis is a conceptual tool often applied in physics, chemistry, and engineering to understand physical situations involving a mix of different kinds of physical quantities. ... Electric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. ...

In SI units, the electrostatic constant (where is the permittivity of vacuum) has to be used. Several other laws of electromagnetism also become easier when all quantities are expressed in electrostatic cgs units; this is the main reason that the cgs system of units is still in use in physics and electrical engineering. The main drawback of this approach is that two other sets of cgs units and equations are defined, the electromagnetic and symmetrical systems (the latter system mixes the first two). The equations in all three systems are usually written in non-rationalized form, so-called because the factors 2π or 4π appear often in unexpected places (in situations not involving circular or spherical symmetry, respectively). It is possible, albeit less often done, to write each set of equations in rationalized form. The word proportionality may have one of a number of meanings: In mathematics, proportionality is a mathematical relation between two quantities. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ... Electromagnetism is the force observed as static electricity, and causes the flow of electric charge (electric current) in electrical conductors. ... Physics (from the Greek, (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and understanding of the fundamental laws which govern matter, energy, space and time. ... Electrical Engineers design power systems… … and complex electronic circuits. ...

The coulomb is an extremely large charge rarely encountered in electrostatics, while the statcoulomb is closer to everyday charges.