Abcoulomb
Encyclopedia
The abcoulomb or electromagnetic unit of charge (emu of charge) is the basic physical unit of electric charge
in the cgs-emu
system of units. One abcoulomb is equal to ten coulombs.
CGS-emu (or "electromagnetic cgs") units are one of several systems of electromagnetic units within the centimetre gram second system of units
; others include cgs-esu, Gaussian units
, and Lorentz–Heaviside units. In these other systems, the abcoulomb is not one of the units; the statcoulomb
is instead.
In the electromagnetic cgs system, electrical current is a fundamental quantity defined via Ampère's law
and takes the permeability
as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.
The definition of the abcoulomb follows from that of the abampere
: given two parallel currents of one abampere separated by one centimetre, the force per distance of wire is 2 dyn
/cm. The abcoulomb is the charge flowing in 1 second given a current of 1 abampere.
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
in the cgs-emu
Centimetre gram second system of units
The centimetre–gram–second system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time...
system of units. One abcoulomb is equal to ten coulombs.
CGS-emu (or "electromagnetic cgs") units are one of several systems of electromagnetic units within the centimetre gram second system of units
Centimetre gram second system of units
The centimetre–gram–second system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time...
; others include cgs-esu, Gaussian units
Gaussian units
Gaussian units comprise a metric system of physical units. This system is the most common of the several electromagnetic unit systems based on cgs units. It is also called the Gaussian unit system, Gaussian-cgs units, or often just cgs units...
, and Lorentz–Heaviside units. In these other systems, the abcoulomb is not one of the units; the statcoulomb
Statcoulomb
The statcoulomb or franklin or electrostatic unit of charge is the physical unit for electrical charge used in the centimetre-gram-second system of units and Gaussian units. It is a derived unit given by...
is instead.
In the electromagnetic cgs system, electrical current is a fundamental quantity defined via Ampère's law
Ampère's law
In classical electromagnetism, Ampère's circuital law, discovered by André-Marie Ampère in 1826, relates the integrated magnetic field around a closed loop to the electric current passing through the loop...
and takes the permeability
Permeability (electromagnetism)
In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. In other words, it is the degree of magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability is typically...
as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.
The definition of the abcoulomb follows from that of the abampere
Abampere
The abampere , also called the biot after Jean-Baptiste Biot, is the basic electromagnetic unit of electric current in the emu-cgs system of units . One abampere is equal to ten amperes in the SI system of units...
: given two parallel currents of one abampere separated by one centimetre, the force per distance of wire is 2 dyn
Dyne
In physics, the dyne is a unit of force specified in the centimetre-gram-second system of units, a predecessor of the modern SI. One dyne is equal to exactly 10 µN...
/cm. The abcoulomb is the charge flowing in 1 second given a current of 1 abampere.