Current, Resistance, and Electromotive Force
In physics, current is the rate of flow of charge that causes a field. The SI unit of current is the ampere (symbol: A). In the SI system, the ampere (symbol: "A") is the unit of electric current, which is the rate of flow of electric charge, and is a dimensionless quantity. Electric current can be defined as the rate of flow of electrons or other charge carriers through a material, such as a conductor. Current can also be defined as the rate of flow of the electromagnetic field through a vacuum. Current is often measured in amperes (symbol: A), or in units of coulombs per second. The SI unit of electric current is ampere (A). The ampere was originally defined as one coulomb per second, its value having been known since the early 18th century. This was an arbitrary standard based on the total charge of a static system at rest, and the unit was then called the "coulomb", a term derived from the French phrase for 'charge of one coulomb'. In 1948, the definition of the ampere was changed from the charge of one coulomb to one ampere, and the old definition of the coulomb was redefined as the amount of charge transferred in one second by a current of one ampere. The symbol for current is I; the symbol for the ampere is A. The SI unit of resistance is named after the Italian physicist and physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first electrical battery. In the SI system, the volt (symbol: V) is the unit of electromotive force, which is the difference in electric potential between two points, and is equal to one joule per coulomb of charge (i.e., one volt is the difference in electric potential between two points that results from carrying one coulomb of charge in one second). The volt is named in honor of the Italian physicist Alessandro Volta, who invented the voltaic pile, an early form of electrical battery. The volt is not an SI unit, and its use is not recommended by the SI. It is most useful when dealing with extremely high voltages, such as electrochemical cells. However, in many applications it is more convenient to use the coulomb (C), the SI unit of charge. The volt is defined as the potential difference across a resistor that has a current of one ampere. The volt is also the potential difference across a resistor that has a current of one coulomb. The volt is equivalent to the joule (J). The unit of potential difference (voltage) is the volt (symbol: V). One volt is equal to one joule per coulomb (J·C). The volt is an SI unit and its value can be expressed in terms of the SI base units or other SI units. 1 volt = 1 J·C = 1 V = 1 W·m·s. The unit of electric charge is the coulomb (symbol: C). The coulomb is equal to 6.25·1018 electron-volts (eV), or 6.25 · 10 C = 6.25 · 10 C. The coulomb is used as a unit of electric charge by some researchers, but this usage is not recommended by the SI.
